Linux gaming support is really at the mercy of the engine Devs wanting to do it. There isn't enough of a market share for it to be "obviously viable" (i.e. stupid not to do it) last time I looked into the numbers.
Both Unity and Unreal Engine are multiplatform enough to support compiling a Linux version of your game just by clicking your mouse -- everything just works out-of-the-box with no extra work needed. That's why there have been so many more Linux games on Steam in the last few years than there ever have before (I remember 10 years ago when the iD Software games were pretty much all we Linux gamers had).
It's AAA games that use their own engines and developers that are too lazy to click the Compile for Linux button in Unity that are holding us back.
> everything just works out-of-the-box with no extra work needed
I would be extremely surprised if that was true for anything other than relatively simple games. No matter what cross-platform abstraction you use, you can never totally get away from dealing with the actual platforms.
