Animals don't wipe, but humans don't want to smell like a filthy toilet. Not complicated. We wear clothes and sit on furniture, neither of which they do, unless humans let them(ew, another conversation).
I have seen animals in the wild and they can be kinda raunchy smelling/looking. Even on a not so well kept farm animal you will see filth. Some animals lick themselves and then lick you. EW.
The difference is that we care. Not that our bodies need more wiping.