An important quote about cults from Hassan backs up what you are saying.
"It is important to understand that in most Bible-based cults, although the member is aggressively taught doctrine, it is not the doctrine that holds him in the group. It is the sense that the group is God's true people, a feeling cultivated by techniques of mind control. " Stephen Hassan, Releasing the Bonds p.145
Few JWs I knew really thought about the doctrine. And of course, if they did it just opens up too many quetions. It is more about belonging to the group.