Haven't they? I can download iOS apps from the app store, sign them again with my own keys for MacOS, run them natively on my MacBook without any issues. Same binaries, same APIs. It all just works.

From what I've seen people have mostly been asking for Mac OS features on the iPad, not phone apps on the Mac.

The increased compatibility is great and kind of obvious given the switch to ARM, but if it went both ways then the M4 chip in iPads would be a lot less bored.