[loeg]

Why would someone design a radio system this way (instead of independent signal to the FM) and what is the risk of running an FM station without rebroadcasting that lead to these rules?

[Anotheroneagain]

I suppose for safety reasons, as AM receivers can be easily improvised. (in some kind of critical situation)

[Kwpolska]

And isn't AM sound quality worse?

[dylan604]

Stereo AM signals are (was?) a thing!

https://en.wikipedia.org/wiki/AM_stereo

[op00to]

AM sound quality can be much better than FM. There are AM pirates that show up once in a while that have absolutely beautiful signals.