I don't know what Linux you're on. On mine I have to actively maintain it. I have to run something `sudo apt update` `sudo apt upgrade` every week or so and then deal with whatever breaks. Conversely, on my Switch and PS5 it does this automatically. I expect the Steam Machine will also update itself automatically. They have an incentive not to break things since it will cost them money to fix all the device they break. Linux on the other hand (not complaining) basically says "not our fault if it breaks". So, I'd prefer the Steam Machine where, I believe, it is their fault if it breaks and they will fix it.
Sometimes there are regressions in the kernel and other driver issues. My laptop is more than five years old and I had to boot an older kernel for a while until a regression got fixed. I guess that's less likely to happen on Windows. Not being as close to the hardware vendors means there are bound to be more edge cases even on boring distros like Ubuntu.
Someone might say I can install Linux on my PC but then I have to deal with maintaining it.
So, what I hope the Steam Machine is, is effectively PC based console with no Microsoft, no root kits, and no maintainence.