Probably for the same reason they don't support every Arch package on the Steam Deck out-of-the-box; it breaks easily and it's not their job to fix it.
Additionally, I think Valve doesn't want to end up over-committed to replacing Windows. They can handle the storefront side and do a decent job with handling the runtime, but actually committing to a desktop alternative to Windows would be spreading their resources thin. It feels like a smart call to not jump into that arena if your hardware products don't need it.
Lots of assumptions that could be totally wrong. Custom distros are not new operating system - majority of hw support is because linux supports it. It would probably be more work for Valve to support only their hw instead of keeping what linux/arch support.
I am also not sure why you think they wouldn't want to end up replacing Windows. Thats exactly what they've been trying to do since microsoft included their store in windows. That is more than a decade long plan in motion which already failed once but they are still at it.
They're not assumptions, I outlined in my comment it was my thoughts and beliefs.
> Custom distros are not new operating system
Nothing is. Windows uses old DOS code, macOS uses BSD code, nobody's OS is truly written "from scratch" in 2025. Just because you can recycle old programs doesn't mean writing an OS is easy.
> majority of hw support is because linux supports it. It would probably be more work for Valve to support only their hw
And much of Linux hardware support is not in-kernel, period. Valve could not flip a switch and start supporting Asahi Macs or Nvidia's proprietary UNIX drivers; they would be committing to patching and maintaining all of their future quirks and surprises. Not even Valve should be wasting their time doing that.
> I am also not sure why you think they wouldn't want to end up replacing Windows.
They do! But "wanting to replace Windows" and "wanting to write the replacement for Windows" are two different things. Valve's current software team has a headcount lower than 500, they aren't equipped to compete with Microsoft even if they wanted to. It's much easier for them to ship all-in-one style devices that keep expectations low and replicate Windows' most desirable features.
> which already failed once
Steam Machine was a home console, it did not replace Windows for anything that wasn't directly ported to Linux. The lesson from this era is simple; supporting Linux is hard. It's hard for developers, hard for consumers and especially hard for Valve.
Additionally, I think Valve doesn't want to end up over-committed to replacing Windows. They can handle the storefront side and do a decent job with handling the runtime, but actually committing to a desktop alternative to Windows would be spreading their resources thin. It feels like a smart call to not jump into that arena if your hardware products don't need it.