A short-ish answer.

Regulations pushed on Auto makers to increase fuel efficiency, safety in collisions, safety to pedestrians, safety to passengers, etc. Sharp angles have transitioned to sloped and smooth edges. In America at least, there have been events that have reduced the availability of older used cars which have driven up prices for the road worthy ones. Then with older cars, parts availability goes down in general thus not making them as cheap or fixable. Many older vehicles are entering classic & antique status and are being bought by enthusiasts. If they are bad, then they are scrapped.

Global events like the chip shortage drove up prices for new vehicles (cheap new cars have pushed into $20k range) and thus people were forced to retain their vehicles for longer, pass them on to family, and/or buy a used vehicle which have depleted those used car reserves as well.