I think many JWs are convinced that "the truth" has the miraculous ability to change people. The reality is that JWs are no different than people in other religions, or even people in no religion. You can brainwash people into going to all the meetings, doing the study, going out in service, even earnestly praying to God, but it doesn't change what people are, not really.
Most people have a tendency to minimize their bad behavior and justify it in their own mind, but then there are some people who are just evil and it doesn't matter how many hours they spend at the Kingdom Hall, they are going to do what they are going to do. The sad part is they usually get away with it because most JWs live in denial and don't recognize evil when they see it because it wears a suit and says all the right things. That's why child molesters get away with it so often and for so long.