Putting on a seatbelt is just another one of those automatic movements you make when you get in the car, along with turning on the ignition. It wasn't always so. In 1984, people were almost as resistant to seatbelt laws as they are now to vaccine or mask mandates. But it wasn't really the seatbelts, any more than it is really face masks now. The world has plenty of people who just don't want someone to tell them what to do, even if it will save their lives.
Seatbelt laws and smoking prohibitions have certainly saved lives, but the vaccines and masks are even more important because your choice to go along with the requirements or not affects everyone around you as well. Contrarians and those who spread misinformation have already caused hospitals to be full, variants to mutate, and children and the immunocompromised to be infected. And they certainly have prolonged the pandemic.