I think it’s also one of those doesn’t-seek-converts plus you-leave-if-you-marry-outside religions. Those two things plus lots of secrecy around actual beliefs

I think it’s also one of those doesn’t-seek-converts plus you-leave-if-you-marry-outside religions. Those two things plus lots of secrecy around actual beliefs and practices (that one’s less of a problem with Zoroastrianism iirc) seemed to always be factors in a book I once read about vanishing near-East religions. Basically mimetic-evolutionary action, if the religion has the wrong properties it’ll tend to decline.