The only non-Windows OS supported by GoG Galaxy 2.0 is Mac OS, and unlike Windows 7, it actually still gets security updates and doesn't have the company behind it actively telling people to stop using it. Windows 7 is on its way out, whereas Mac OS is not.

I don't know why it would necessarily be the case that people who refused to upgrade their OS would be more likely to want to run older games. Regardless, the fact remains that Windows 7 is unsupported by Microsoft and therefore is increasingly a security risk, and while there are certainly issues with Windows 10, running an OS that isn't getting security updates is just plain stupid unless you don't have it connected to the internet. For GoG to test Galaxy 2.0 on Windows 7 not only would require additional resources (which they're clearly short on), but it would require running insecure computers to do their testing. And plenty of other software companies have been refusing to support their products on Windows 7 for a while now, so GoG is far from unique in that respect.

On top of all of that, because GoG Galaxy is not required to install or run any games from GoG, GoG has that much more leeway in which OSes they support with GoG Galaxy. Even if GoG Galaxy 2.0 didn't work on Windows 7 at all, that would not prevent anyone from buying, downloading, and playing their games on Windows 7 - just like the lack of a Linux client doesn't prevent people from downloading and playing GoG games on Linux.

I don't know how people come to think an OS is suddenly insecure just because the manufacturer stopped support a few months ago, which they even didn't, support is just not free any more. There's still paid LTS (increasingly expensive), so they didn't stop all work.

Windows certainly always has had issues with security, but with a bit of care and use of Brains 1.0 there is not much to be feared.
And even if a really bad 0-day remote exploit would occur - MS would fix it, even for outdated Win 7, just as they did for XP for WannaCry (2017) and the Remote Desktop exploit (May 2019!).

MS can't afford to leave Win-7-users in the rain if a serious issue arises. Even with declining market shares that's still millions of machines.

So running Windows 7 is not an increasing security risk - it will be only when a) an exploit shows up that b) requires no user interaction and c) is not fixed by MS.
IMO running a stable, hardened Win 7 (Pro or Ultimate) is more secure than running the "I'm permanently beta and update if you want it or not" Windows 10 Home, especially with the abysmal quality MS has delivered in the last few years... And yes, before you ask, I work in IT.

It actually does work on Windows 7, I have it running on my PC right now and I use 7. I had some issues when installing it but that was due to all the security software I have loaded on this PC since Micro$oft cut support. To this day, the only issues I've had with Galaxy 2.0 have been centered around the massive amounts of security software I use on this PC.

Maybe I got lucky, but I think the "only Windows 8 and beyond" thing is false because it runs with no issue (beyond common bugs) on my Windows 7 PC.

After it went EOL, Microsoft has only fixed security issues for XP in extreme circumstances. Any OS that doesn't get regular security updates is increasingly at risk of being infected with something, because the more time that passes, the more unpatched vulnerabilities are found. The risk is of course much lower for Windows 7 now than it will be later, and good computing practices can reduce the risk, but they can't eliminate it. If you want to run an unsupported OS and take the risks that go with that, that's your prerogative, but ultimately, you're just asking for trouble, and don't expect anyone developing software to spend the time and resources required to make sure that their software runs on your outdated setup.

There is never zero risk, outdated OS or not. Of course it's up to the users to keep track of known vulnerabilities and act accordingly. It should be this way regardless if the OS is old or not, because 0-day exploits can always happen. The only difference is that those "holes" will be fixed on a current OS eventually, on an outdated one possibly never by the manufacturer.
I'd say someone who consciously decided to stay with an old OS and is aware of the responsibility that brings is potentially safer than the average user who doesn't care and relies on not being hit in the time between the exploit and the patch - which is a pure game of luck.
And even with the patching - considering the sometimes abysmal quality of MS' patches in the last few years, which you often even can't prevent from installing - it's sometimes even better to not update. See https://www.forbes.com/sites/gordonkelly/2020/02/19/new-windows-10-update-starts-causing-serious-problems/ - and that is not the first time a "security updates" hides, removes or outright deleted users' files. You really want to say this is "safer" than using Win7? When forced updates potentially destroy your data?
As I wrote, I work in IT, and we have Windows 10 at work. My machine is set to postpone updates as far as possible, but every time a bigger Win10 update is out there is at least one of my colleagues' machines that makes trouble. From "death after reboot" (OS destroyed...) to data loss to annoyance like missing programs we use, deactivated or missing services of our GIS - you name it.
The same goes for Visual Studio, which is actually an amazing development environment - but every third or fourth update breaks something (at least you aren't forced to install them, so usually one of us tries it for a few days, then either greenlights it to the rest - or not).

It's up to the developers to decide if the market share of an old OS is worth the trouble. As I wrote above, using Win10 in the current state of MS' QA is also "asking for trouble". It's astounding how a company like that can become this unprofessional.

To be fair...

Epic: Used to be Epic Megagames, became a powerhouse in the industry, created one of the most mainstream industry standard game engines and a number of the biggest titles in the gaming industry... and is now known best for the disaster that is the Epic Games Store.

Valve: Has spent more than 6 months burying their heads in the sand over the fact that they turned the Steam client into an active health risk for many users with migraines and epilepsy. Actively refusing for over 6 months to even publicly acknowledge the problem, let alone roll back to the last known stable version, instead pushing forward in spite of their own total screwup.

GOG: Recently decided, in the middle of a shutdown of their support service, to force a beta build of their client onto the entire userbase in spite of knowing it's still in beta AND in spite of having an almost, if not entirely, absent support platform. Currently appear to be totally oblivious to the complaints about it.

Not like MS has anything resembling a monopoly when it comes to hilariously incompetent decisions affecting computer users lately.

Neither Epic, Valve, let alone GOG have a monopoly on an OS which people have to use to earn money, get work done and which runs on infrastructure-critical machines. You're comparing toy vendors with the developers of airplane avionics here.

And Microsoft isn't "technically" a monopoly, for about the same reason Steam wasn't "technically" a monopoly while having a similarly ludicrous percentage of their respective market share. And I wasn't saying that those examples were as critical to the computing industry, only that they are industry leaders in their respective - and also computer-related - markets. And that they're doing stupid things with a level of stupidity that rivals MS, even if not with the same scale of impact.

MS is not critical to "the computing industry", they're critical to everyday life. Imagine your doctor losing all your patient data, because of a botched Windows update. All the screaming of "they should have made backups" or "they shouldn't have used Windows in the first place" doesn't help when you're turning up half-dead and they can't say what medication you're allergic to.

And MS/Windows is technically a monopoly in many areas since most specialist applications run exclusively on Windows. If you work in certain areas and are forced to use the software - no way around Windows. You can decide to not use Steam because games are not essential, but you can't decide to not do your job because the software only runs on Windows.
MS has manoeuvred themselves in this position on purpose and often enough with not the nicest (or even evil) business practices. And they're still doing it. They basically bribed the city of Munich to abandon LiMux - a lighthouse project of using OS software in public administration of a metropole.
They wanted to have Windows and Office in every one's life - and now they have. But they also have the fracking responsibility to keep things working. You can't compare this to Valve/Steam, unless you want to compare Boeing to Revell.

windows 7 is over 10 years old and you can upgrade to the newest windows for free. stop trying to create a problem when there isnt one

Do you even read the posts you're answering to? This was referring to the current state of affairs at MS, the really sloppy QA, the hideous quality of their updates their current systems.
Problems like these: https://www.forbes.com/sites/gordonkelly/2020/02/19/new-windows-10-update-starts-causing-serious-problems/ which is not the first time Windows-Updates destroyed users' data.
On a colleagues machine an update destroyed the OS, the whole partition was gone after the restart (luckily the data was on a different drive and could be salvaged). Windows 10 Unprofessional I say...
Right now we're struggling with KB4556813 on Windows Server 2016 which kills our GIS users database on our client's machines for no apparent reason. This is ridiculous!

Win7 eol'ed January/2020. I've been running Win10 since 2015 and have never seen a reason to go back to Win7-- Which actually seems clunky and old and slow to me now. Win10 also has support for much newer hardware than Win7 supports. The only thing good about Win7 today, imo, is that it's better than WinXP...;) I've never had a Win10 version destroy my data--not once--and I've run every version of Win10 since 2015 as an Insider--not even the beta versions I've tested have destoryed my data! Never lost a partition, etc.

IMO, Win10 is far better than Win7.

Couple of things:

1. I'm playing devil's advocate here, and have at no point suggested that the problems with gaming companies are comparable in SCALE or SEVERITY to what happens when Microsoft screws up.

2. When addressing the context of similar behaviours, you absolutely can compare examples from vastly different situations with vastly different severity and scale when there are other similarities at play.

And I don't think you can. When your game crashes you don't get your entertainment. When your medical software crashes or your airplane control system, people's lives are at stake. Stakes and responsibility are not even on the same scale even though both are technically "software". That's why development, QA processes and validation and certification (the "behaviour") are completely different, or at least should be.

If you don't think that's possible, you are objectively wrong.

It is POSSIBLE to compare the leader of Germany in the late 1930s and early 1940s to a puppy if there are colour patterns in its fur which look like the man's distinctive moustache. That doesn't mean you're saying the puppy is that person, or that it endorsed his actions as a leader. It's possible to compare the actions of a company whose products are used in scenarios of extreme importance, note that they're behaving like their product has no more need for serious QA handling than companies who are the equivalent of toy manufacturers, and note that those toy manufacturers are also doing a worse job than would be reasonable to expect from their industry. And it's even more relevant when both the primary company you're comparing and the secondary ones you're comparing them to are involved in industries with some measure of overlap.

Like, for example, noting that yes, Microsoft are screwing up on really serious things, but also, other less societally important computer software developers who shouldn't be held to the same standard are failing to meet even the lesser standards they should be held to.