It could be because of the fact that the fighting type is "strong". Superpower, close combat, focus blast, focus punch, high jump kick, Meteor assault, etc. Then on the other hand, a weak fighter essentially is nothing, it cant help much: Karate chop, brick break, rock smash, etc. There isn't much of an in between, and so there aren't very many in between 80 power moves. Oh, and I wanna add, submission can be learned by a decent amount of Pokemon, but it has 80 accuracy and has recoil, so its like worse than power-up-punch