In my experience migrating build systems is always way harder than you'd think because you kind of have to do it all at once, everything depends on it, and they're usually pretty hairy. Also testing them is very slow, and they're a moving target.

It's also difficult to justify time spent on it because so many people are like "but it works already".

They already moved away from pure Make in Android 8, wonder if that was just more urgent or the migration to Bazel is just harder?

It's interesting to read about the original announcements to port to Bazel, e.g.:

https://www.infoq.com/news/2020/11/android-aosp-bazel/

...it reads like one of those overly optimistic 'process optimizations' a middle manager new to the team would come up with after having a look at 'the accumulated mess'.

Maybe said middle manager moved on, with the rest of the team letting out a sigh of relief and carrying on with actually being productive ;)