One big problem with FM is that it is selective. If you have two different signals of similar strength on the same frequency you won't get good reception from e

One big problem with FM is that it is selective. If you have two different signals of similar strength on the same frequency you won't get good reception from either. With AM you'd hear both. If one signal is slightly stronger on FM that's the one you'll hear, with AM you'd hear both. For music this is an obvious choice, better to pick a signal than have them interfere, but for emergency communication the opposite is true. It is easy enough for a human to hear two conversations and pick the one you want to listen to by focusing on it - we do this in crowded rooms all the time.