That would be quite the power move, but unfortunately Steam doesn’t hold that much power alone, I think. There are still enough games that are not on Steam. As of today , Microsoft is the biggest games publisher (with Bethesda, Blizzard, Obsidian, ID, Mojang etc. belonging to them) and there are also giants like LoL or Fortnite.
True, but for example for Win7 they dropped support last year I think. So quite some time.
Yes and no, people can still use win10, it just won’t receive patches anymore. And in this particular case, my best guess is, that most people would rather use and outdated OS for a long time, rather than changing the OS altogether. Not every game is on steam, also not every non game programm is easily available for Linux. Humans are lazy.
OP clearly overestimates how many people would use SteamOS or any other Linux distro for that matter. Most users are casual gamers these days, they are not changing OS just because there is a forced Windows update.
Yeah that’s true, I think the biggest hurdle are games that use anticheat that don’t work on Linux, which are afaik usually multiplayer games. So they might be able to pull gamers, that only play Singleplayer games.