To answer you in a different way: Today we would build these systems with FM or digital voice. But there are enough advantages we've gotten used to (graceful

To answer you in a different way: Today we would build these systems with FM or digital voice. But there are enough advantages we've gotten used to (graceful degradation, better handling of doubling, etc...) that it's not really unequivocally a win to switch to FM. There would be downsides that anger existing users, and it would be expensive, and the net benefit would be relatively small.