Typically the Java APIs are restricted to the bare minimum Chrome Android needs to do sandboxing and native code-gen for V8. Shared memory only works in a more limited way with many less options. They'd really like to restrict these APIs way more and not allow apps any way of loading dynamic native code with the exec bit set, but can't because of Chrome and antitrust worries about just making Chrome system software with access to the APIs it needs that a competitor couldn't replicate in an APK.
I think you can see some of their thinking with the removal of exec; they just want to undercut termux because that isn't needed for V8, but as long as loadable generated native code is still needed for Chrome, termux could potentially create their own ELF loader to replace exec).
Exec should just be behind a separate permission anyway. A flashlight app has no legitimate reason for exec()ing random code that was not in the APK bundle, but the permission should be there so that JIT's and stuff like Termux can make use of it.
