He's probably confused because nobody ever does on TV for some reason. Like on come dine with me etc or those documentaries where people go to meet their long lost families.
Maybe it used to be legal not to? I would have thought one of those situations of it being legal not to wear one, but still stupid not to wear one.
It's possibly due to the responsibility issue. In a normal car age 14 is the cut off. For children up to 13, if caught with no seatbelt it's the driver who would be fined. For passengers of 14 and over the passenger themselves would be fined. I know this is generally why children are exempt from using car seats in taxis, along with the practicality aspect.