Different types of hair and skin cells in those locations.
DHT causes it generally - it is a powerful sex hormone, body, and facial hair growth promoter that can adversely affect the hair on the head. Also maternal and paternal genes play a part.
So whilst adolescent boys are gettin' jiggy with the increase in DHT to make them rampant neanderthals with bum fluff tache's (vellus hair) - the downside for many is the onset of baldness to the crown.