As an additional, Steam was there first, if that counts for anything.

Another reason is the Steam platform is a very open platform for developers. They are given a wide range of logistical tools to determine how and why their products are selling. It's something no other distributor can really compete with.

The main reason I think is simply because everyone is already on Steam (since Steam "got there first" and most people are fine with it) and not really interested in using GOG (aside from fixed-up games or exclusives), so the vast majority of money is made there. So why bother releasing here, especially if more money can be made creating a new game rather than getting the current game onto GOG.

I encourage people to use both to support competition, but given Steam's marketshare, I shill for GOG currently.

This isn't really a problem on the r/gamedeals subreddit anymore now that the "GOG doesn't sell Steam keys" autobot post is bold and obvious. (Whenever a GOG sale is shared, the bot automatically posts that message in the thread.) However, yes, when Witcher 3 came out and were giving away GOG keys instead of Steam, there was a lot of salt. :P

Steam has an advertising budget? news to me.... not like other DD sites who try to use streams, youtube, blogs etc...

Probably, budget may not have been the best word. I meant they get plenty of advertising via people using their client word of mouth etc.

all this + a lot of ppl still don't have a clue about anything. Look at some answers over there http://forum.battlefleetgothic-armada.com/viewtopic.php?f=3&t=537 or anything no matter where on paradox as soon as you mention "steam free". You'll get tared, feathered, lashed and dangle from the gallows next to a jolly rogers before you even had the chance to point out that gog.com is a legitimate shop and not pirate bay 2.0.

Why the fuck would a pirate ask to get a game released to a shop that he could pirate somewhere else anyway.

I can agree with point 2 and 3, but 1, I can hardly say that there is no evidence of such. I'll be honest here, but I once tried to search for Star Wars: Republic Commando on Piratebay and the GOG version of the game appeared in the list. Not only this game, but also other games' titles coming from GOG have made their way to pirate websites.

You know, that is such a shame too. I'm sure that GOG relies on the maturity and honesty of people who honor their agreement here not to put any of their versions of games out there for others' to use. However, it would be interesting to see the statistics of the pirating of those games made available by GOG versus those games that were not released through a DRM-free site.

To say that thieves didn't exist at all would be a misstatement.

Gog's releases are certainly the easiest executables to pirate, but Steam games always end up on pirate sites regardless since the default DRM method is so trivial to crack. People who aren't interested in paying for a game, for the listed price, just aren't gonna pay for it. At that point it's irrelevant whom they pirate the files from.

I would add (and it basically expands on (2)):

4) Auto-updates are appreciated by devs.

5) More direct control for devs: Updates, control of sales and discounts.

6) More ways to encourage gamer interaction, such as cards, drops and Steam Workshop.

7) Steamworks. GOG has its Galaxy equivalent, but it's in pre-release, less well documented (far as I know) and more limited.

I think many players are just fans of Steam and want all their games on Steam and provide max support to Steam.

But the second problem is not have any single front end for all those shops front end. I have bought games two times because of the confusion between the multiple shops.

That's the only way for all shops but Steam, single front end for all of them and integrating as well than possible Steam too. There's been a ++ Steam client NOT made by steam, for sure it had often problems because of constant changes in Steam client. It was just the web version but still it shows it's not totally impossible.
The points to cover:
- Complete library from all shops, and including shop origin for each game, eventually no shop origin at player wish.
- Global play profile with all games time from all shops.
- Much better Game library organizer than any shop client provide.
- Quick access to any shop registered by the user.
- Indirect links to install games forwarding to shop install management. Possibility for shops to integrate better with the front end including a custom page like with suggested similar games and so on.
- Indirect links to launch games forwarding to shop launch. Possibility for shops to integrate better with the front end.
- Include communities with multiple formats.
Any single shop but steam would benefit of such approach, just because there's steam.

Later eventually Steam will have enough pressure from enough gamers to also integrate better to this single front end.

some people are smart when they buy

8) Because developers here can't steal from their customers/fans, by forcing a game to have content removed at will upon copyrights expiration at a far later date than purchase day, like how GTA Vice City and San Andreas did on Steam! How can the developer steal from you here, if you back up your games and you fully own them?
9) Because GOG allows YOU to select which game version you want to play (depending on how early you backed up your game, plus soon the rollback feature on Galaxy will be on). We can't have players deciding which version of the game to play, now, as a developer, can we?
10) Because devs don't believe that a bunch of retro-maniacs, people who lived through the golden age of pc gaming and have played complex masterpieces that were the pioneers of gaming genres, could "appreciate" enough and sink into talent-less, horrible, new, trendy, consolified, oversimplified, crappy ports, while shouting "shut up and take my money" and white-knighting the spineless devs, like how all those amusing, refreshing, circus performances, run on Steam...

There, the list is complete, now!