It's a liability issue. Say someone gets hurt from a seatbelt. If it's designed exactly as required by regulation, there is an immunity for the company (IANAL

It's a liability issue. Say someone gets hurt from a seatbelt. If it's designed exactly as required by regulation, there is an immunity for the company (IANAL so I don't know the legal term for this) IF you try to make it better, and do make it better for most cases, but worse for some edge case, then you have a liability issue in that your 'negligence' caused injury that wouldn't have happened otherwise. The stance on civil liability in America often stifles innovation in many areas regarding life safety. Tesla is learning this quickly.