Idk. Probably because you can get away with drawing them more cartoony? There's loads of animals in the word so it's bound to look like something. As for humans, limited.
I totally love the art style too! In the original pilot that was never released to tv, it was actually going to be a different art style! I do like it, but I'm glad they stuck with the other one :3
Link
Tyrenai
Better than anything I can do, I've been drawing for like 6 years and hardly any human experience at all :P