Catholicism, Greek Orthodoxy, Islam, and a few other religions include the concepts of clerical hierarchy and official texts, which helped them become organized religions. These are the faiths that survive today as widespread and major influences. Pagan religions like that of the ancient Greeks, Scandinavians, West Africans, and Mesoamericans are (in some cases) older and more ancient than their counterparts, but never got around to organizing, reforming, and dominating. Why is that? Related to this question: https://www.reddit.com/r/AskHistorians/comments/2yzyg9/reformed_pagans/