nobody is out here running a plain Linux kernel and maintaining a UI stack while AOSP exists.

Wrong, that’s even why I bought a PineTab2, PinePhone, and a reMarkable and use them pretty much daily.

Are there a lot of these compared to Android? No, but please do not say “nobody” when you mean “most” or “the vast majority” because by doing so you are reducing the perception of choice. Some people, like me, DO prefer plain Linux when they can. By hiding the fact that commercial solutions do exist this is helping an already dominant solution.