I thinks it’s really just normal human resistance to change. I do remember being resistant to seatbelt requirements, mostly because it seemed so unnecessary and uncomfortable.

Even knowing the statistics, I didn’t have family who had been in an accident where the seatbelt would have helped - plus of course I wore a seatbelt (in front). It was interesting that being in the back seat was always different somehow, but you also don’t always have inertial reel or adjustable belts, so I wonder if it comes down to convenience and comfort