I have thought about this for much of my life, certainly ever since I became a serious Unitarian Universalist back in the 1970s. For a long time, I assumed it was a lack of information or education that kept people loyal to very conservative theological paths. But as I've spent time in ministry, become acquainted with good people on a wide variety of religious paths, and examined my own reasons for leaving conservative religion, I've had to change my thinking.
Quite a few people whom I respect and love are devout members of conservative religious communities with theologies far different in many respects from my brand of liberal UU mostly-Christian thought. Many of them are well-educated and committed to serving others. Except for theology, they're not that different from me, though we diverge on some social issues.
As I sat in a local restaurant this morning, finishing my breakfast coffee, I started a list of the reasons I think people choose (or remain in) conservative religious paths. Here it is, in order of how they came to mind.
1. They were born into it and see no reason to leave.
2. They make a bargain with God during some crisis.
3. They marry into it and are devout to satisfy their mate.
4. They are willing to believe religious authority figures (pastor, priest, etc.) about doctrinal matters.
5. They stay because of family unity.
6. They are not very self-reflective or critical of doctrine.
7. They lack information or they reject the information they do get.
8. They want to belong to a popular religious path.
9. They reject liberal social values.
10. They are rebelling against parents.
11. They work at jobs that give them little or no time to reflect on religious doctrines.
12. They have distaste for the Other whom their religion considers sinful.
13. The foundational story of their religion is gripping and the consequences of diverging from its tenets are frightening.
14. They fear that the story is true and this keeps them from abandoning it.
15. Their religion allows them to act in ways that they enjoy while forbidding them to act in ways they fear.
This is not an exhaustive list and there are overlapping reasons. If you think of more or if you quibble with any of them, please comment. I also jotted down lists of "why people reject conservative religious paths", "why people come to liberal religions" and "why people come to Unitarian Universalism". I will blog on those lists another time.