The problem is - linux (outside on server land and maybe SteamOS) is everything but (regular) user friendly.
When people buy a new phone the expect a smooth experience without any major inconveniences and uniform UI. And apps. Lots of apps. Full of features and mature UI. Linux mostly have none of it.
Consumers didn't pick up Windows Phone or HarmonyOS enough to matter either. Access to the two common app stores is crucial for user adoption even when the UI is good.