Android built a new, giant moat for Linux (or "Linux" depending on your opinions about Android) in the embedded application processor space - now the "standard" board support package target for new embedded AP hardware is almost always some random point-in-time snapshot of Android. Running "mainline" Linux is hard (because the GPU and media peripheral drivers are usually half-userspace Android flavored stuff and rely on ION and other Androidisms) and bare-metal is even worse (where previously, you'd get register-level documentation, now, you get some Android libXYZ.so library).

I don't remember there being any time in history where you got "register-level documentation".

Those boards were always accompanied by horrific binary blobs glued to a kernel form a stone age. Or Windows.