Deck works because most games are self contained, allowing them to have a default game mode that bypasses the desktop entirely.
Right now Steam Deck works because of a focus on a very specific use and users. A general purpose desktop requires a lot more, and right now even the most mature linux desktop (GNOME, Plasma etc) have their rough edges and learning curve.
https://www.youtube.com/watch?v=Pzl1B7nB9Kc
I'm not really following desktop Linux, is Linus' assessment still accurate?
Churn (and consequent ongoing immaturity) seems to be the price we've paid in the last 10-15yrs of "progress" making them suck less. I hope it settles down a bit soon and we get to enjoy more longer term polish on these improvements though.
What do you have in mind specifically? GNOME 3 is very mature, and has a consistent, polished design that far surpasses Windows 11. In fact, in view of recent macOS redesigns, I am tempted to say that it surpassed it too.
PC does have a fair amount of users that want it to operate in a console-like way when it comes to usability, the moment you tell them to fiddle with a runtime or experiment with the command line variables you lose them. That's to say nothing about handling stuff that lives outside steam, because PC gaming shouldn't equal Valve. The Deck is a nice manageable subset to deal with and fairly small enthusiast audience
Let's say, hypothetically, that Valve releases SteamOS to the general public, and it's received generally well, and it becomes much more common for people to use "that Linux thing" than it is today. Then let's say, hypothetically, that Valve turns evil and... I dunno, starts charging money for updates? At that point you've got a large population already using Linux, I'm sure there would be a pretty big migration to Ubuntu or some other mainstream Linux desktop.