I don’t think there’s that much of a long game. They give money for old cars because they:
A) can still sell it for profit, and
B) mark the living shit out of cars so they can easily absorb a few thousand $K to make a deal. Even more if the buyer finances it because the dealer gets “incentives” from the banks, etc. to sign new deals.
A more interesting mental exercise, imo, is considering how many times a car is sold over its lifetime.