Not entirely correct, the simple reason is called "money". Windows is by far the most used platform in the world, because of this also the most potential users of the gaming industry. Linux has almost 100 different distros and much of these don't accept other than opensource apps in its repository and only very few modern games are (2?...3?), there isn't much more than FPS and arena shooters with graphics of 20 years ago, side scrollers and other with pixelgraphics, crappy RPG 2 D or with isometric view, few exceptions apart, like the above mencioned The Dark Mod, despite that it isn't full OpenSource because of some non-free art assets which included and for this is tecnically only freeware and for sure for this, not in most of the repositories. Making games is a lot of work and there are not much idealistic game devs out there which will make a modern game for buy me a coffee. That is the main problem because Windows is still the best platform for games and not for tecnical reasons.