money

Its "well known" they use players for advertising and dont want the spread of low quality screens and streams.

Part of it is incompatible technologies. They are building for consoles and mid to high end PCs. For what they're building, they can generally only take away so much visually and still deliver. Some settings can only go so low, and realistically, there are so many possible bottlenecks they'd have to account for, it would be difficult to build the game for modern machines with support for old machines running outdated software on poor hardware.

Part of it is they don't give a shit about people who can't buy a newer machine at $400 US to run their games, because if you can't afford that, you can't afford to feed the machine that is modern gaming.

Part of it is publicity, as was mentioned earlier. They don't want people producing terrible screens or gameplay footage of their beautiful new money machine. It could hurt mtx sales.

And finally, part of it is because you touch yourself at night. Shame on you.

Support mainly, as it requires using older API's that may not be supported any more.

You can turn the graphics down quite a bit more in many modern games by tweaking the config files. There are several YouTube-channels and subreddits dedicated to this. Some even go as far as looking like PS2-games with enough tinkering. Stuff like decreasing internal rendering resolution, dropping texture quality below the levels you can choose in-game, disabling effects.. The results can be very surprising.

I mean, probably it's not feasible enough, paladin made a very nice points...

It's because developers are classist bastards, they don't care if the poor can't afford to play their games.

Potato Mode :D

Yes, well, but the real problem is when developers create a game that visually is into 2005 standards, or fewer, but needs a Witcher 3 machine era to play it smoothly.

Laziness aside, a large chunk of the problem is a lot of modern game engines are now so heavy-weight they just don't scale down well. Eg, many 2015-2020 games like Control, Dishonored 2 or Deus Ex:MD when run at low resolution / preset both look worse yet still run 3-4x slower than 2010-2015 era UE 3 era games maxed out because the heavy-weight engines just don't scale downward that well. Examples:-

Dishonored 2 and DX:MD on "Low"...
https://i.imgur.com/rRlT94C.jpg
https://i.imgur.com/Oa5wjdD.jpg

(look at the houses at the top-right for Dishonored 2 and the police uniform in DX:MD, general lack of anti-aliasing, lack of anisotropic filtering on the floor, etc)

...and yet both still run 3x slower than Dishonored 1 and DX:HR maxed out on same low-end hardware:-
https://i.imgur.com/ZdamYye.png
https://i.imgur.com/sAmZv7Q.jpg

In fact, this made me LOL the other day (compare the paintings on the wall), as it highlights just how badly optimised modern games are for textures even on "Low" vs 90's games fed with community HD texture pack mods...

It's a conspiracy. They want to push the specs hard so only the l33t can afford and play it.

No, it's more complicated and less crazy than that. When you design a game you have several ideals in place: what the game is about, how it is played, how it looks, and how it performs. In theory you could base a new game on a framework which is highly flexible with effects and performance, cutting back on every detail just to make the game "run" on outdated and frankly backwards hardware.

But to design a game that way is incredibly time consuming, expensive, and not the way devs approach games. And even if you could, you're basically asking a dev to destroy their artistic vision and sacrifice "how it looks" in favour of "how it performs".

There is a point in a game where "potato mode" looks so god-awful there is no point in playing it. If a developer decides a minimum recommended specification I'd expect a decent playable experience for it. For anyone below that spec, that's not what the game was intended for. The trick is not expecting that new games will be forever compatible with your hardware, but rather that there will always be games you can't play right now because of your budget.

As others have said... money.

What it sounds you're looking for are "demakes", versions that are signiificantly lower in specs than the original game. Take a look at the Lucius demake and its description:

"Lucius game has been demade, and is now ready for mayhem. Enjoy all the gore now in fewer pixels and fewer colors. The original game has been fully demade to achieve the atmosphere of an 80's style gory adventure. Lucius is now killing all the pixels and there isn't a damn thing anyone can do about it."

Not completely sure but the requisites of this demake seem to be higher than the original Lucius.

Yeah money and publicity: they don't want their games to be portrayed in the media as godawful-looking and the effort it would take to scale down the game visuals wouldn't be worth the time and money put into it.

And then, provided the game can be scaled down to a point that can be run on low end machines, would there be a return of investment significative enough?

This right here.. well, it's not necessarily the game engine but the game itself.

When you have complex geometry, scaling it down to an arbitrary potato level without completely breaking the game is fa from trivial. Naive attempts will have horrible results, for example you wouldn't want entire buildings and walls to vanish and then pop into sight.

We've seen this in Crysis, where you can see a guy at the distance and empty two magazines at him and he won't even flinch. You wonder why, creep forward a few meters, and then a giant boulder pops in between you and him. Yeah that explains it. (This is supposed to be the easy case, but they still managed to screw it up)

There's so much more to speeding up graphics than just scaling down textures and picking lower LOD for models. Same for every other aspect of the game (physics, AI, etc). A lot of work for the designers and programmers. Why spend all that time and money to cater for a terrible experience? Even if you can just stop drawing objects, you will still need to simulate the parts that affect gameplay somehow.