By that logic, SteamOS is not a selling point of the Steam Deck

No, by my logic, Valve does not sell SteamOS, which is correct. Much like Pop, it’s freely available to install on any machine, including Framework.

By your logic, Linus would hate SteamOS too.

And yes, they do sell it on their laptops:

Is this photo supposed to prove something? I don’t see a charge for PopOS?