They don’t run unsigned binaries, but they run self-signed binaries (to the same extent that Intel Macs run unsigned binaries) and the linker automatically does the signing. It’s an architectural simplification, not a substantive tightening of the screws.
Programs on Intel Macs can do some funny things to invalidate their code signature in was that Apple silicon won’t support, which I guess you could call a change. But I agree that the transition was probably mostly made for simplicity.
