I think the idea is that no amount of forking Android is going to produce something different enough to entice developers to port their apps to it, but maybe if an entirely new Linux-based mobile platform kicks off, there's a chance?
If you have to consult `developer.android.com` (a Google-owned domain) to develop for your "totally not Android" platform, it may be difficult to avoid the temptation to do as the documentation recommends and simply embrace proprietary Google services and hardware attestation and whatnot. After all, 99% of users have those things and it's just these several weird forks that don't?