It’s a statistical thing, although there is some speculation that the REASON for the statistical anomaly is that people who don’t buckle up are more reckless. It just happens that people without seat belts are slightly more likely to be in an accident.
I also speculate that it could be that, if you aren’t wearing a seat belt and you have to swerve to avoid something in the road, you can lose your seat and therefore control of your car, and swerve back into other people. Being buckled in makes it easier to maintain some level of control of the vehicle. It’s hard to keep steering your car if you just flew out the window.
oddly, i believe they also showed that motorcycles without helmets had fewer accidents, although the result of those accidents was much more severe. I presume being able to hear what is going on, but who knows? It could all just be the random statistical bounces falling a certain way.
People who don’t wear seatbelts are more likely younger and/or more reckless. You are confusing causation with correlation.
People without helmets probably feel more vulnerable (I know I would), and have use a tad more caution.
These two may seem to contradict, but I don’t think they do.