Think of paint like skin, kind of. When a car gets freshly painted, or when you buy a new car, the paints generally still in a stage of de-gassing, where all of the gasses from the paint are slowly releasing. If you start covering it in polish/wax, you clog the "pores" on the paint and get imperfections.
I've always been taught not to wash a car for 3-6 months after a paint job, although some paint shops have developed baking techniques to get the gasses out faster.