I used to think that maybe it was just the people who were raised in the truth, especially from infancy. They didn't know what life outside of the Organization was so it was all they had to cling to. But that's obviously wrong because many, many have left--happily--never to return.
But you have some people who worship the WBTS and who are consumed by it. No bad thing can ever be said about the organization or its members. In my house I am usually ripped to pieces by my wife if I say anything "negative" about the organization or the brothers. Doesn't matter what they did. Because they are part of God's Organization, they are free from accusation or even inspection. The Organization could write "kill your husbands or children in their sleep if they don't fully submit" and she would do it. I have no doubt of this.
These people refuse all logical thought and accept everything the Watchtower prints as one hundred percent undeniable truth. Most of them hold the Watchtower and its literature in a higher regard than the Bible itself. How else can you explain why they are so accepting of the Watchtower's ever changing doctrines even though the Bible (even the hacked JW version!) is always constant.
Are these people just weak minded? Do they lack inherent ability to make their own decisions and depend on others to rule them (sheep)? Is there some other psychological issue there that makes them more likely for total commitment than others?