First off, I would like to say that I was raised a JW so I can't speak for those who actually joined up by their own free will...
I think one of the most important factors people are missing is FEAR. Fear may not be what has gotten them in, but it is what keeps them there. And that fear can be of different things.
The fear of change. This isn't something exclusive to religion. It applies to all aspects of life. What if you leave and things don't work out?
Fear of losing family, friends.
Then there is the "what if" syndrome. What if they were really right? Am I not trusting in Jehovah with all my heart? Am I leaning upon my own understanding?.... blah blah.
I'm an atheist, so I could just cross of JW's from the question asked and throw in the name of any other religion. Clearly it would not be fair for me to ask that question because there are certainly smart people who have a belief in other religions as well. It was touched on by a few people, but to reiterate...If more rank and file jw's were aware of the Watchtowers background more eyes would be opened. But in order to do that, they would have to relenquish the fear of looking for the "truth about the truth" which is equated with inviting demons into their minds.
I have seen quite a number of threads questioning the intelligence of JW's in general. Though I find myself questioning the same thing sometimes, I realize that calling people stupid is surely not a way to get them to open up their minds. When you have the same shit pounded into your head continuously for 10, 15, 20, 30 years, it isn't easy to try and prove it all wrong. Even if you notice a few inconsistencies, you have to weigh the "pros and cons" of any decision you make regarding your sticking with your beliefs. >>>>> yes, I am rambling and haven't really focused my thoughts on the original question which I no longer remember in its entirety..plus it is 2:20am.