Funny fact: Amorous was playing with the idea in the beginning to have Miles being a beast dude. But since many people freak out if they can't play as a human (as if 24/7 RL gameplay as a human isn't enough already) he didn't want to take that risk and went with a human Miles.
Back to topic: Quite a few people don't like the idea of having infertile CBs. One theory I have is that both species (humans and beasts) are already barely a match when it comes to mating so the problem gets worse with each cycle and the human <-> CB or beast <-> CB is already too much to work anymore. Plus it's stated that both humans and beasts see CBs as inferior species so they are barely willing to fix the whole problem when it comes to storytelling.
Maybe it might change in the future but then Amorous has to rewrite quite a few things and that will cost time and he doesn't have that much already.