Personally, though I don't care for them, I can understand the reason for the weirdly slender bodies: conventional standards of beauty. You notice it in art, too. People want their characters to look pretty, so they apply human ideals to a lion... hence, skinny animals. Just a theory.
The rest... yeah, I got nothin'. I don't think spaghetti noodle legs can be explained that way. Small issue, though, and the game is fun enough to make up for it.