And I know several hard core UNIX guys that *don't* run Windows, and run AAA games.
Just making a statement and saying "the end" is pretty pointless -- I've seen the benchmarks, some games were running higher framerate in Linux than Windows. Some weren't. I wouldn't switch OSes over it to chase framerates or anything. But the graphics stack internals, the drivers themselves, and Wine and Proton's direct3d and Vulkan support, have all improved drastically in the last 5 years and especially within the last 2-3. Even the Intel graphics chips finally have had the bugs worked out (not that I recommend gaming with them, most of them are still a real dog performance-wise, but they now will run the games (or "walk" them depending on how bad the framerate is....) rather than crashing or showing a corrupted screen.
Valve has focused on Linux for years, because a few years ago they thought they'd ship out all these steam boxes, and now for shipping the handheld. They don't want to spend $50 a console on Windows, so they've spent on developing Wine into Proton, and improving Linux's video stack, for the last several years, and it's seriously paid off.
Why would you use an OS for gaming that barely has any games? Well, games run fine through steam and wine so there's plenty of games. So some people don't want to deal with Win10's telemetry; they build a system or mod it too much, find Win10 didn't activate and don't want to pay or pirate Windows when they don't have to; some have hardware that worked better in Linux (the multi-head example for one), and some just don't like Windows so they don't have to deal with it.
My main point though, no matter what OS you run, there's plenty of room for fine gaming to be done somewhere in between the 8W or so the mobile Vegas use and the 400-500W these new cards will suck down.