Several reasons, none of them good.
• Baldness research is seen as a waste of time and resources; the "just shave it, bros" only compound this problem.
• Most men don't care (and many still don't) before the age of the selfie.
• The FDA and other archaic administrations
• People bitching about "ethics" where the words "stem" and "cell" appear together in the same sentence.
People have been trying to cure hair loss for thousands of years.
The reason a cure has not been produced yet is because science is not advanced enough yet to cure the problem.