That's fair. I agree that it would be nice for them to properly release SteamOS for general hardware. I think valve probably doesn't want to get roped in to providing tech support for hardware platforms they don't control beyond what they do for steam.

My impression is that their priority is building the hardware to show what's possible in the form factor, then get third parties to buy in to the ecosystem to keep it going (which we're seeing with steamos support for the Asus and Lenovo handhelds). The software has to be polished and well-received to get this buy-in, which is easier when they have control over the hardware.

Their strategy with the original steam machines (circa 2015 I think?) skipped the first party hardware step and they didn't do well with the software execution either- although iirc that's where the big picture mode, steam controller, and generally better controller support came from.