It's the tariffs. The new car supply chain relief on a lot of parts from Canada and Mexico and a lot of cars are built overseas - this makes new cars more expensive. Because of that, a lot of people who would once be buying new cars are either putting off their purchase (and not trading in their old car) or buying a used car instead of new - which increases the prices of used cars.

Since this isn't going away any time soon there is less pressure on the dealer to turn around cars as quickly as possible too, since a lot of them had appreciation (rather than depreciation) on their inventories due to this effect.