Of course, benefits aside, the main reason was gratitude. Most of the Nascent Soul Stage experts in the world were there for similar reasons, at least in name, although the reality of things might be a bit different. The sect had raised them, and given them opportunities to advance to their current stage, so out of gratitude if nothing else, they should remain behind and defend the sect!
That being said, no person could be fed on just gratitude and thanks, there was naturally a system in place that made that gratitude very easy to feel, for instance, follow up techniques and methods that were required for their cultivation, or perhaps holy grounds that only the one sect possessed… When a person was raised in the system of a sect, they would suddenly find that if they were to leave it, their life would become very uncomfortable, and even the small benefits were quite major.
