I think it's largely to do with the whether the games are PvP multiplayer or not. I.e. many such games have anti-cheat systems that embed in the Windows kernel (or something like that - my Windows internals knowledge is... slim).

I assert that most people who're happy running Linux on their desktop (for games or productivity or development) do not overlap much with the people who're happy to take kernel patches from UbiFuckingSoft. And this includes those people who're willing to take closed-source NVIDIA drivers.