Not sure, but, my educated guess is that it will be more efficient as they improve Rosetta 2 to do this on demand instead of pre-translating every app on the store every time Rosetta 2 is updated.

Even if that means the users have to retranslate, that's still essentially "free" (to Apple) distributed compute.

Apps installed via MAS and packages are pre translated (at install time)

So is this a little bit like Android apps being translated into Java Byte Code at install?

It’s the other way around: an intermediate state of compilation is uploaded (basically the internal state after all non-machine-specific optimizations have been done, like hoisting invariants out of loops, etc). The App Store finishes compiling with the flags for the various CPUs supported (iPhone 6, iPhone 12, etc).

translation of most apps doesn't take a significant amount of time, and have it pretranslated would mean shipping code that was not signed by the app developer.

But isn't apple store already re-sign applications code with apple's own key so they can do stuff like this? Or is it only on iOS?

iOS definitely does this, optimizing for the different supported devices. I hope they start doing that with future Mx macs.