On the other hand, there’s been a bug open to make a simple harmless change to fix this in Android for 9 months, with no response from Google other than asking for reproduction steps as far as I can tell.

https://issuetracker.google.com/issues/371713238

Some comments on the bug accuse Google of intentionally not fixing it to make people buy Pixel Buds instead of AirPods.

I wouldn’t say that myself, but then again I also wouldn’t say that Apple intentionally violated the spec just to make AirPods not work on Android.

Buganizer is not where you submit code to be reviewed and accepted into Android. And by the author's own admission that change is a hack and not a proper fix. Anyone is free to make a proper fix and upstream it if they wanted to.