The number of vehicles on the road that are older than 20 years is shockingly low, especially American brands which rust considerably faster than others. Even cars from 2000 are rare.

In places where there's no extended winter weather I've noticed the cars are often older, with 40+ year old junkers from the 1980s looking, by local standards, no more than ten years old.

The point is it takes time to eat the car away, in which time the car begings to pollute more