Have they introduced some other mitigations, for eg UAF, to improve memory safety?
It seems possible that nixing MTE is to prevent stomping on some TLAs exploits?
In terms of mitigation of UAF, a great deal of new code written for Android userspace these days is in memory safe languages such as rust. Also, a lot of testing with instrumented code sanitizers is still done before release. We don't know how much risk MTE actually mitigates.
The massive amount of Linux kernel and Android memory corruption bugs is well known. The positive impact from good integration of MTE on this is very clear and compelling. These aren't unknowns as you're portraying them. Apple has understood the value of it and made great integration into iOS. The positive impact is very clear.
The vast majority of low-level code in Android is still in memory unsafe languages. That includes nearly the entire Linux kernel which is the core of the OS security model. MTE in synchronous mode combined with other protections working alongside it is one of the few realistic ways to make Linux kernel exploitation much more difficult.
The massive amount of Linux kernel and Android memory corruption bugs is well known. The positive impact from good integration of MTE on this is very clear and compelling. These aren't unknowns as you're portraying them. Apple has understood the value of it and made great integration into iOS. The positive impact is very clear.