I think it comes down to Maslow. Especially for people born in like me, you tie some of the higher level psychological needs people have into belonging to the organization, and it is very hard to leave it even if you want to. For others who are recruited, the organization meets their need for belonging, and especially for men who are discouraged from gaining status through outside acheivements like work, attaining status inside the organization by becoming an elder, CO, DO, etc is very alluring.
Once they get to Bethel, they have the adoration of people who don't even know them, and are given money, presents, influence, etc. If someone is a born-in, and dedicated their life to Bethel, even if they thought it was a scam, I could see them staying for the free ride and because making it on their own on the outside is difficult, and once they reach a certain age maybe impossible.
This is how I explain to myself some of the elders who are so awful. You have men, who are discouraged from gaining status in the usual way (work, education, acheivement) and you give them a title and a little power. This is their only way to meet that natural hunger for esteem. Couple that with their lack of education and training in pastoral care of people and you have....JW Elders who bully or sometimes abuse their flock just because they can and have been divinely appointed to do so.
Really it meets even the highest level of need, self actualization because that is where morality lives. And JWs are nothing if not moral. So, this is why disfellowshipping has the effect that it does, and also why leaving is so hard, and why staying has such pull. When we talk to "true believers" this is what we are talking to - their need for belonging, esteem, and self-actualization - not just their belief system. This is why it is so hard to get people out...and to leave ourselves if we try.