That's what gatekeeping is for. It's to keep out anyone who is not a member of the ruling class who is willing to kiss the right rings and genuflect with the right mentors. If you dare challenge the establishment from the outside, they will circle the wagons.
Lol. If you challenge the establishment from the inside, it also doesn't work. It doesn't matter if you yourself are ruling class or even rich. But the reasons for not taking Goldstein's serious is a combo of many things: safetyism, "no factual evidence" compulsion, traditional problems of unorthodox vs conventional methods, corruption/cronyism, self interest preservation, tall poppy syndrome, cowardice, legitimate fear or reprisals/license threats, etc. Lots of reasons. Most probably is that other regular doctor's just aren't willing to try his drugs since they only have his word to go on and many are powerful, higher risk drugs. They would have to dive deep in to the science to understand all the biochemistry/mechanisms, which they don't have time for/aren't capable of understanding, for them to prescribe it. Plus, they couldn't defend their actions fully if hey came under scrutiny for it.