I've been this way. And for me, saying something about the seatbelt would have been because knowing he wouldn't wear the seatbelt would hurt my feelings. I would have felt that if he would wear the seatbelt that would show that he loved and cared about me. So I would expect him to wear the seatbelt and would tell him so. And then, if he didn't, I would be hurt and equate that to him not loving or caring about me.
But in truth, whether or not another person wears a seatbelt has nothing to do with ME.