Why does SUV's and Hatchbacks have Rear Windshield Wipers but Sedans do not have one?

Have you ever noticed that there is no Windshield Wipers on Sedans  but SUV's and Hatchbacks have one. The reason is simple, as a car moves forward, the air that flows over the top has further to travel than the air passing underneath. This causes a reduction in pressure of the air "falling off" the back of the vehicle compared to the air passing underneath.

This variation in pressure causes the air exiting from under the car to move upwards into the lower pressure area. It brings with it dirt, moisture and debris from the road surface thrown up by the wheels and easily sticks to Hatchbacks but not in Sedan.

A sedan also has a lower profile against the air and is more streamlined. This has the effect of reducing turbulence and causing fewer air vortices behind it and throwing up less dirt and moisture.

At the times of Rain the rear windows of Sedans which is like mostly vertical, doesn't get that much rain, because you're driving forward. Very little water actually land on rear window. Another factor is the trunk itself, which helps move air along and not circling around the rear window, trapping dirt and rain. Air flows past the roof and flies for a bit then drops onto the trunk.

SUV's and Hatchbacks with windshields right at the rear has nearly vertical windows, but not the trunk to guide the airflow. It has a low-pressure zone right in that area when it's moving at speed, which will "suck in" water and dirt and thus make the window very dirty.