Makes sense. Trucks are less aerodynamic and the weight is not distributed as evenly. Probably easy for the bed of the truck to catch wind, move around, and lift due to being so light in relation to the front of the truck. Once that happens lift off is not far behind. Whereas, with a car, the air just blows over the top of it. I’d imagine if the winds get strong enough to move cars too, ones with windows rolled down would be the first to fly.
One Ring to rule them all, One Ring to find them, One Ring to bring them all, and in the darkness bind them.