Why don't voice radio communications use FM?

So, it might be a safety issue - using FM would effectively filter out
the weakest stations that could be heard if AM was used.
Under what conditions would you need to hear really weak AM stations?

Let me think. If my radio died and all I had was a handheld I would
really want to be heard... even with this tiny antenna.

Mind you, this is just a theory. Most of my time in the air (and 100%
of my solo time) was in gliders with no radio at all. I just happen to
know a bit about the technical side of radio :-)

Bartek