Why did Zoroastrianism begin to disappear in the seventh century A.D.?

Zoroastrianism began to decline in the seventh century A.D. primarily due to the Islamic conquests, which led to the fall of the Sassanian Empire and the subsequent spread of Islam in Persia. Many Zoroastrians converted to Islam under social, economic, and political pressure, while those who remained faced discrimination and marginalization. Additionally, the centralized Islamic state promoted a monotheistic faith that overshadowed Zoroastrian teachings, contributing to its gradual decline.