I don't have any more specific information as my obsession with MPD has waned over the years, but the rationale for drug companies is basically if a drug doesn't make some Billions of dollars than its considered a failure. With limited money to spend for research it makes financial sense to spend it on drugs with the highest potential. Hairloss drugs haven't done well in the marketplace mainly because their effectiveness is limited along with a difficult regimen. But that is enough to deter drug companies from continued research.