I'll just add on that BSG are a horrible example when it comes to delivering on "promises" and plans.

If memory serves, the official plan is still to do a steam release when EFT is "out of beta". But they realized they make a LOT more money if they control the whole store so... Which is likely why they moved away from Steam Audio, continue to use their grossly incompetent anti-cheat solution, etc. Nikita et al will "heavily imply" they are doing stuff and then just ignore it because people keep buying top tier accounts so they can have maximum storage and so forth.

Also: SP Tarkov works REALLY well under Proton. Something about the new gui for the spt-installer needs more dependencies to work again, but the actual game runs great if you can be bothered to manually patch it.

Tbf most devs probably want to do it, they just can't justify it financially. Most games' programmers are computer nerds, and they would be the ones in charge of implementing that kind of stuff. They'd happily do it because obviously, as computer nerds they love Linux, but even if they accept to do some unpaid overtime just because they really want to implement this, it might get blocked by the publisher because they don't want that kind of stuff to bypass QA especially since it has a chance of affecting all users, and when looking at the numbers, it's just not profitable to them.

Now the steam deck could change that dynamic because it has a decent market share, and I would love to see the actual numbers but I'd be willing to bet that most deck owners buy more games than the average player.

Source: am games' programmer, computer nerd, and steam deck owner

Tarkov is in a different much more complex situation. It uses some Battleye addons that are custom made for the game that Battleye will not port to work on Linux.