I completely agree. Ideally, we'd have a fleet of recent model year cars on the road, and would utilize them very heavily so in 5 years, they have ~200,000 miles on them and are near the end of their life.

I know an older couple with two vehicles from 2008 with 36k and 54k miles on them. They are in great shape, always parked in the garage at home, etc. While their natural life might be 150k, it's very likely they will be in a junkyard before then. Part availability becomes an increasing concern.

From an environmental standpoint, old cars were manufactured under less stringent emissions standards. At a certain point, the emissions required to manufacture a car are more than offset by the marginally lower emissions from a new vehicle.