Why Are There Inside Rear View Mirrors In Class C's

I have my rear window covered, so the mirror is worthless except for seeing inside the house, if not for that limited use, I'd remove it altogether, it's not required in many states anyways as long as you have both side mirrors , I can't see out the rear window in the mirror anyways, even if it weren't covered.
But I have the two side mirrors and the rear camera which work very well.