Why are all the A&O mga lobo so skiny?

It's just the way the decided to do it. And (I need to watch the movie again lol) Humphrey's fat friend was chubby. Also real mga lobo aren't really big either.

Well, in the movie the packs were struggling for food, so making them look emaciated kind of adds to that. It shows that they don't get enough pagkain so they're all skinny.