Other posters here seem to misunderstand what AOT means in today's Java. It just means caching some state. There's still a JIT involved, it's just warmer.
You're thinking of Google as a single top down company. It isn't. Think of it as an anarchy of warlords where each pulls the strings and management doesn't really know what's going on.
Flutter made a lot of sense during the Oracle lawsuit when Google needed a way to show Oracle that it can pivot from Java. Now it no longer makes sense but the inertia is too deep.
My guess is that flutter is sold internally through the Huawei support as a leg within China.
There are other solutions that give you MUCH faster startup with lower memory e.g.: https://foojay.io/today/java-server-work-before-startup/
Edit: it seems I missed that 28 added the actual native code compilation phase so it will probably be closer to the GraalVM numbers in the link above.