I'm reading _Religions of Iran_[1] right now and getting a lot out of it. I think the reason Iran doesn't get talked about is simply because it's too complex and it doesn't boil down nicely. In addition to Zoroastrianism (the surviving type seems to be an entirely different branch from the one that was at one point a state religion), there have been huge numbers of Jews, Christians and Buddhists(!), to say nothing about religions that appeared and disappeared (Mithraism, Manichaeism) and tiny religions that were once larger (Mandaenism) or little ethnic religions that still exist in small pockets (Yezidism, etc.) Sometimes, the rulers were religiously tolerant; other times they were not. Even when they were not, they document their difficulties homogenizing the population; Iranians are apparently private enough about these things that they can exist as undercurrents for hundreds of years or longer. This, on top of the fact that there have been several Iranian empires over the millenia.

The author of the book is surprised it hasn't been studied in more depth, and I agree with him. It's a very interesting place.

[1]: https://www.amazon.com/Religions-Iran-Prehistory-Richard-Fol...