In 1994, the economist Laurence R. Iannaccone published a paper entitled "Why Strict Churches Are Strong." In the paper, Iannaccone explains why strict, conservative churches are stronger and their memberships grow faster than less strict, liberal churches in the United States, a long-term historical trend first documented by Dean Kelley in his 1986 book Why Conservative Churches Are Growing.
Iannaccone suggests that the strength of strict, conservative churches has nothing to do with their theology or even with religion at all.
So only individuals who are very committed to their faith and their church would join strict, conservative churches, because they are the ones who would not mind all the rules and regulations just to be a member of the church.
As a result, members of strict, conservative churches stay with their church through thick and thin. In contrast, anyone can join (and leave) less strict, liberal churches because on average they are less committed to the church. In other words, strict, conservative churches are stronger because they screen their members more carefully.
You immediately recognize that other organizations (whether knowingly or not) also employ the same logic to maintain strong membership. The reason you must endure so much hazing during Hell Week to join college fraternities and sororities is that they only want truly committed pledges to join.
Obviously, if you are willing to make a complete fool of yourself, and, worse yet, potentially risk your life and limb, just to join the fraternity or sorority, you are very committed to the house and its membership. Anyone less committed (and more sane) would not go through all the hazing just to join.