Because black men know when to give it the fuck up and shave that shit instead of lettin their hair receded and bald until it's 10 inches long but their hairline is behind their ears lol don't come for them.
What about dreads, braids , high tops and fades? Not ALL are bald. Many men in general, not just black , tend to keep their hair cut low period. "Why do most men keep their hair short?" would be a better question. It's like me asking "Why do all white elementary school boys have bowl cuts?" when it's obvious that not all do.