One interesting point I've seen online is that the steam machine is more of a budget Mac than a pc. As valve controls the whole stack including the OS which creates a very streamlined experience that just works.
Maybe its what will make Linux more mainstream!
Yes, sometimes it's difficult to find the correct driver for Linux and set it up. Having steam machine be start and play like steam deck really brings the console feel on PC. Moreover it's still Linux which you can use for other things, so people doesn't feel loss for this.
Valve's vertical control over SteamOS, the UI, and the hardware specs indeed gives the Steam Machine that taste of Mac. Not sure if Apple would have gone for something like that if they ever made a console: one key difference is that Valve keeps it open like a regular PC which is a major benefit to keep the device alive down the road for years to come.
It doesn't control the games though, hence Proton.
If they controlled the whole stack Linux native games would be a requirement.
It was always the disconnect between the people who made it work and the people who couldn’t that prevented wider adoption.
Linux has gone mainstream a long time ago - from dvd players to android phones. It just hasn’t succceeded on old preexisting markets ( personal computers ) but has taken large parts of most of the newly created ones ( servers , mobile devices , embedded devices etc )