The bigger problem is wasting developer effort contributing to Google's platform. The real secret behind Android being "open" (sorta) is that while almost nobody runs AOSP, Google has tricked a bunch of fools into working on Android forks instead of building a real competitor.
Playing at their table is a losing game, the house always wins.
The developer effort is not wasted because it's open source. Anyone can fork it at any time. None of it can be thrown away from humanity, wasting it.
The reason why no one runs AOSP is because the phone market rewards differentiation. Each phone manufacture wants to build their own experience and building on top of AOSP is how they do so.
Is it really a losing game? Building a new OS from scratch is not worth it. Why throw away an entire app catalog for your device? Consumers want access to existing app catalogs when buying a phone. If anything is a losing game it's building a new mobile operating system over forking Android as a base.
Windows only isn't still 90% market share because of Wine, then Proton.