How is gaming on Linux limited? You can still play proprietary DirectX games with open-source API translators, and arguably Linux is a better development target than MacOS or Android. Even relative to Windows, Linux can play a lot of games that are broken on modern PCs (like Diablo 2 or Fallout 3/New Vegas). Similarly, having an open-source compatibility layer opens up opportunities for community optimizations, which happened with games like GTA 5 and Elden Ring before the same patches got released for Windows.
Why was DirectX, the proprietary API, more successful in the first place? Because it did other things besides graphics as well? Was the graphics API better? OpenGL is reportedly buggy on Windows nowadays, but why?