Stupid people do not wear seat belts.
Stupid people get wasted at family events, get into fights, and then to show how macho/macha they are, attempt to drive a car.
I've read car accident fatality reports in my area carefully for the last 20-30 years. In many cases when people under 30 are killed, the accident reports say they were often thrown from the vehicle and crushed by the car or smashed their heads on the road or off road objects. It means they weren't wearing their seat belts.
I don't know what the percentage of teen and young adult drivers who wear seat belts is, but I would bet it's a lot smaller than the percentage of older adults who use them.