[derefr]

Cars are devalued by mileage because the average car is taken care of so poorly that small damage accumulates into big, irreversable damage over time. For example, waxing wears off -> unwaxed surface pits -> rust forms -> holes form. If you re-wax the car often enough to prevent it from ever pitting, you'll never see rust or holes no matter how long you own the car. Same for most of the other components.

Individual drivers may not be able to take very good care of their cars, but large companies that use fleets of cars can take them regularly (perhaps even every night, as their default storage) to maintenance garages and have them restored.

[ghaff]

Except that, in practice, rental fleet cars are typically only kept until they have fairly modest mileage and then sold off.