If we're being realistic from a business standpoint: Linux is at best, 3% market share. A very passionate 3%, but 3%. Using resources to support such a niche sector is a hard sell.
3% of millions of people is a massive number of people. Given how easy recent work on wine has made porting from windows, it's really hard to defend not having a linux version, from a business standpoint.
I'd hope this community of all places would understand that "just integrate X with Y" is never as simple as "just". It's still something a team needs to do, and the gain is minimal unless Epic is also going to try and make their own console-esque device. That's the incentive for Steam.
Going by the Steam hardware survey, 3/4 of Linux users were not using Steam Decks when they got polled. So I’m not sure if a console-esque device is actually required. A large part of the reason why Linux usage is growing, is probably that it mostly just works these days
Yes, it's not the most optimal business decision as a software company to invest in hardware. The clear move is to either grease Microsoft's palms, or let then outright acquire Steam (or Valve as a whole). Valve not doing that is either in part ideological, or part very long term thinking on the best financial path later, instead of now.
But at the same time: while the ends was "be independent from Microsoft", their means at first was very Microsoft esque. Partner up with hardware vendors, make some Pcs with Steam built in, and brand it as such. Didn't work. Their goal had to be to roll their own hardware because that's what was needed to get the ball rolling (as well as a form factor that accompanied a desktop instead of competed against).
The problem for an also-ran app store is that you need every user you can find.
Linux support may not be a huge deal in the overall market (although it's growing due to the steam os devices) but it's just one more element to Steam's moat.
It's a glorified wrapper around curl, wine and a webview, a few interns could knock this out in a few months. For "3% market share" (growing every day, thanks to Valve) its a no brainer, but Sweeney has no brain.