I had a statistics class in college in which the professor postulated that the driving force behind every revolution except the American one(s) was the result primarily of the governed people repopulating at such a higher rate than the governing people that they overtaxed the ability of the governors to care properly for the governed. The governed couldn't find work to support themselves, especially in times of agricultural distress - so rather than starve they revolted.
It was a fascinating theory, and I think there is a lot of truth in it. I think, also, that there is an element of truth with that idea in relation to religion. I think religions die or stagnate when they no longer are relevant to the masses - when the needs of the masses are not met by their religious leaders - when the leaders lose touch with what is important to the members. Frankly, however, the opposite is true, as well - that religions can die when the masses lose passion for what the leaders teach and demand only what they want to hear.
If it was only about leaders teaching what members want to hear and will accept, it would be easy - but no real growth would occur, in most cases. Members like to blame leaders for the decline of their religion, but, as often as not, it's the members themselves who cause the divide and disconnect - in numerous ways that are not the focus of this post.