Because they had that huge V12 engine in them with a high ratio rear axle. One set out in a wrecking yard here in Cheyenne made out of a convertible coupe with the boom comng out of the trunk. It set there for at least 20 years next to a 1939 Buick convertible that I wanted so bad I could taste it. Finally they all disappeared because somebody came though town and bought every collectable car he had. Mitch