I can offer one example:
ABMP will insure a therapist who provides proof of training in Ortho-Bionomy even when the therapist is not a CMT, as long as the person has met the minimum hours requirement for our method. Some folks want to practice different styles of bodywork or somatics without being massage practitioners.
I do not know if AMTA does such a thing, I imagine they do not. Never have had much interest in joining them.
Also, ABMP offers a discount to Ortho-Bionomy members, $50 off per year, which we appreciate.