As a very bald man, let me assure you, hair does not merely keep growing other places. The exact same hormones that cause the baldness make it start coming out of unexpected places like weeds in a sidewalk. So cool. /s

As to why hair follicles work backwards specifically on the very top tip of genetically predisposed individuals, I can't say. There's a lot of information on the Wikipedia, but probably more we're yet to discover. I know it's still an active area of medical research. Especially active, even, because it's an old white/asian guy problem (usually).