They don’t really have to. They’re still private right? What are they going to do with even more money?
It actually feels good that the 30% cut Steam takes out of my purchases partly goes to improve my Linux desktop experience. Better for me as a user than if they were taking a smaller cut and focusing on Windows only.
1: Valve has been sponsoring work on Wine, Wayland, KDE, mesa gfx drivers, dxvk, and others.
https://www.gnu.org/philosophy/nonfree-games.en.html
Obviously kidding, Valve's efforts will IMO greatly expand Linux's target audience which is laudable. Seems to me that limitation was one of the main pullbacks for Linux adoption, especially in non-developer circles. Requiring dual-booting just for games on the Windows partition is not a convenient band-aid, and Stallman's solution never was one at all.