No mirror lets you see right behind the back bumper. It’s dangerous.
They don't make laws to force cars to add features for convenience.
They reckon the mandatory backup camera law saves 95 lives a year.
Some cars do have remote-control drive features these days, so you can reverse it from outside the car, but that's a super high-end feature (designed for getting in to and out of extremely tight city parking spaces) and relies on the chips that are in shortage, so that's not a solution.