This thing has been true for years, and there are a few things out there that reinforce it, unfortunately.
One reason is the supposed danger associated with some specific herbs. For example, on Susan.org, in the HRT section you can find:
"You may not discuss Pueraria Mirifica or Diane-35 on this site at all due to their being linked with serious health complications."
People are scared to death from the stories of blood clotthing that "happened" with PM. The reality is that any hormonal threatment of any potency comes at a risk of blood clotthing, so PM doesn't have to do with it more than any other herb or pharma HRT (even if HRT is usually done while under medical observation, which is always a good idea).
Another reason is the "Trannier than thou" effect. Many people who have been on herbs for years before deciding that they wanted to transition, compare the cost and power of pharma HRT with herbs, and start telling everybody that nothing but HRT is a valid choice. These people are usually the ones that insist you are trans for wanting breasts, or for wearing bras, or for crossdressing... I think that there is some trauma associated with their coming out, and that they feel the need to defend the "only holy way to fem" which would be to quickly transition with HRT at the first sign of femininity. If you suggest that you want to take it easy or even just to live as a NB or male presenting person whiile wanting some breasts, they flip because the notion is somehow painful for them. It's balck or white, with no grey in between.
Anyway, even if these people resurface every once in a while, they then tend to disappear as soon as they make peace with themselves. Obviously, the annoying stigma on NBE frequently outlives their internet rants, and some more will come in the future.