It is a matter of education.
Has it been properly explained that it is mandatory to wear a seatbelt at all times?
Do his colleagues all wear a seatbelt all the time or is there a rather lax view of the word "mandatory" in his office?
It is a simple fact that a lot of people don't wear a seatbelt. They think they are rebels. They think they are cool or hard or whatever.
They plug the seatbelt into the passenger side to avoid the constant beeping. Everyone knows it goes on.
Every now and again there is a big hoo-ha about it when someone gets caught and then it dies away again. (until the next time)
The societies of consumption and squandering of material resources are incompatible with the idea of economic growth and a clean planet.
