Voltaire explained that the problem lies in the institutionalization of religion. In order to become an institution a religion must determine who is in and who is out. This focus tends to produce polarizing ideas and attitudes, us/them thinking, and can result in a siege mentality.
Most Pagan belief systems simply weren’t amenable to institutionalization; the Pagan beliefs of my heritage (Cherokee) were about maintaining balance and harmony with nature. There was, and still is, a great deal of diversity of beliefs among the people, and very little organizational structure, it was a way of thinking and a way of being, rather than a formal set of creeds or a “religion” per se. It just didn’t include the necessary characteristics by which you could emphasize inclusion or exclusion. It isn’t prone to institutionalization, and it just doesn’t plug into the internet in any way.
Keep in mind also, Native Americans did not have a written language for most of the history and development of the subject belief systems, it wasn’t till the 1800s when a Cherokee named Sequoyah created a way of representing the Cherokee language in written form. So there’s no book, no lists, no set of creeds that can be referenced or disseminated.
It was a Spiritual wisdom that was not transferred by a book, it is a wisdom that was directly experienced in succeeding generations, it was fluid and diverse, It was about religion alive, growing and evolving in time, the idea of institutionalized creeds and dogma would be completely foreign to the way of thinking.
Pagan belief systems are fundamentally synchronistic, rather than the boastful contrasts of institutional religions, I think they have historically moved forward through borrowing and exchange, mutual help, cross-fertilization, cooperation and collaboration. To the question of where they went, I think the answer is, they didn’t go anywhere, they are hiding in plain sight, so to speak.
Today, the Cherokee Nation is predominantly Christian, but the historical belief system that was a way of thinking and being, didn’t go anywhere, it just became a way of “understanding” and “practicing” Christianity. You have Cherokee Christians participating in a broad range of pagan rituals and practices, most who participate in the Green Corn Ceremony are Christians. Fundamentally, the Native American Green Corn Ceremony and the Christian Easter Celebrations are essentially the same thing spiritually.
A lot of fundies will see that and say we aren’t Christians, to which I would reply, so what, Jesus was one of us, He was not a Christian either. Perhaps most religions are practicing the religion of Jesus, as opposed to a religion about Jesus.
There are a lot of different spiritual paths but in the end, they all lead to the same mountaintop.
1 Corinthians 7:7
For I would that all men were even as I myself. But every man hath his proper gift of God, one after this manner, and another after that.