Just for spite. Male hair loss usually starts with a receding hairline followed by thinning on the crown. The two balding areas often connect, exposing skin in the shape of a horseshoe.
Hair follicles are still alive on the top of the head, but they're no longer growing hairs. Hair follicles on the back and sides of the head, however, aren't affected by DHT, an enzyme that shrinks hair follicles. They continue to grow hair at a normal rate. Then, you get the monk look.