If you want to create a design for a product that has to be sold as often as possible, you got to focus on what could be interesting for customers. Therefore, a modern and new look is a good option to make a product more attractive - and that is just what the car industry did since they started to put tons of metal onto four wheels.
As an example we take a closer look at an American steel monster from the late fifties - a Cadillac 62 :
After WWII came the cold war and with it a new era of war planes - Jet fighters.
Inspired by this new technology car design in the US knew just one way: cars have to look like jet fighters!
Her you can see the back of the Cadillac:
"Wings" on a car with integrated tail lights in "rocket" shape are hard to find in any other decade. Also "jet turbines" were added to the car. If you would cut off everything above the door line and remove the wheels you'd look at something with the shape of an old jet fighter.
But it wouldn't be a real American thing without exaggeration.
One could think they really tried to fly with those: