Mind control is the answer as others have pointed. There are many JWs out there who don't really understand what they believe in and those are even harder to show the truth. I am noticing for example, that the hispanic JWs are more indoctrinated than the English ones. Just last night in our book study the question was asked "Who is the FD&S?". Two sisters answered "all of the anointed" and the elder conducting the study commended them for their good answer and never corrected them. Finally one of the other elders probably could not stand this inaccuracy and raised his hand to clarify that since 2013 the FD&S is the GB.
The more dramatic the attack, the more they will attach to their belief and loyalty. Is how mind control works and that is why is such a powerful tool. The mass exodus could be a great idea but it could get out of hand if we don't take the right approach.
There is also a bunch of those who faded for other reasons but they have no idea about TTATT. There is quite a few in my family. They don't attend meeting, they celebrate Christmas and birthdays and all of that. Yet, they keep posting the daily text to facebook and refuse to take a surgery because of the risk of a blood transfusion.