I think it is how you were raised.
"Mom and Dad, why do I have to do this?"
"Because that is how we do things and if you don't then..blah..blah..blah."
Conditional Behavior modification at it's best.
There are very few, if any, who went into religion on their very own without any kind of religious influence in their background, whether it would be family, friends, or the thumper at the door. Those that have were most likely in a very sad, dark place emotionally and needed some kind of crutch to make it and once they set foot in the congregation they get the positive reinforcement they needed. It's all brainwashing pretty much. Not like a Charlie Manson, but in a more subtle way.