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If penicillin had been tested on guinea pigs we’d not have antibiotics - or in a best case scenario, they’d have been developed far later, which would have been disastrous when you consider during WWII people (including doctors & pharmacists!) were attempting to make their own penicillin due to a combination of the scarcity of the miracle drug & the media giving the impression anyone could knock up a batch with a few basic ingredients.
There is doubtless money to be made from creating a surgical technique for successfully grafting a penis onto a transman. All current “gender reassignment” techniques are, as I understand it, considered experimental: each surgeon doing things their own way, with no agreed methods &/or standards of practice. Surgeons working in this area will frequently refuse to fix the work done by other surgeons; so if you travelled abroad for your initial surgery & suffer complications on your return, good luck finding a surgeon nearby to fix them. This may be a - horrificly warped - attempt to come up with something that will become standard. (For avoidance of all doubt, I do not think it is ethical, reasonable, right, &/or justifiable in any way to do this research.)
As @UtopiaPlanitia pointed out, women’s healthcare is massively under-researched & under-funded. We’re still stuck with male as not simply default but prime - nobody rushed to create a new oral contraceptive for women after it was decided the poor men couldn’t be expected to endure a fraction of the side-effects women are scolded for complaining about, for example!