That's because a lot of used car sales p2p, and in cash. Reason being, normal people usually do not have terminals to pay by card (which has limits as well), and doing a wire transfer is somewhat risky. Either because the seller is left without money nor a car if the wire transfer is stopped by the buyer, or the buyer is left without a car and money, if the wire transfer goes through but zhe car doesn't show up. Sure, that can be resolved, but it is a major pain. Exchanging cash for keys and papers so is saver for everyone involved. And depending om zhe car, the amoints can he pretty high.
Car dealers, used or new, are different so.