I think that the assumptions that people join cults for gaining knowledge is flawed. Most people don't care about knowledge and truth.

Take scientology as example. Luke Muehlhauser about taking scientology 101:

This class - a religious class I took as an atheist in order to achieve an unrelated goal - turned out to be one of the most important classes I have ever taken in my life.

Most science classes on the other hand don't teach lessons that the student can afterwards use in his daily life. Science 101 is boring to a lot of students.

Most students of science classes don't feel like they get knowledge in the class that they has an immdieate effect. Religious rituals do something to people.