I guess
Mardavij might have expanded something like this (give or take):
Because the Buyids used the same power base as Mardavij, they were his successors, sort of.
They used Daylamite Iranians, held Shāhanshāh title, etc.
The Buyids were Muslims, not Zoroastrians; but they and their followers were closer to shiism, so here religious minority ruled over religious majority.
May be Mardavij was mad as a cow, when he wanted to revive Zoroastrianism. Or may be it was a sound decision; as we don't know how deeply Islamic was the region. May be he saw that in many cases Islam was only skin-deep (or none); and could be replaced by the revived Persian imperial pride and ancient honored Iranian religion - Zoroastrianism.
Mardavij died too early, so it was all over before it started...
A few centuries later the non-Muslim Mongols ruled the region, they murdered caliph, sacked Baghdad; their support was from the non-Muslim groups only - Jews, Christians, etc. And by that time Islam was firmly imprinted on the local population.
Here Mardavij with his Zoroastrians might rely on the Iranian Renaissance, patriotism, unstable newly converted Iranian Muslims as well.
The Byzantine hold against the whole world of Islam for half a millennia; they can make a good ally to the Zoroastrian Iran together with Armenian and Georgian Christians, why not?
Actually the unity of the Muslim world is somehow exaggerated. Let's take Crusader kingdoms - some of the Muslim entities allied with the Christians against their fellow Muslims.