First of all, witnesses are manipulated into entering the cult, none of them has all the facts when they join, and don’t have a clue who and what agenda is running this corporation. As far as they are concerned they have just being offered a free bible study, no strings attached.
From then on they are being subjected to propaganda, manipulation, and strong social pressure. Some leave but some are not strong enough, don’t have enough support, or just can’t for various reasons.
The fact that they are not allowed to voice them, doesn't mean that they don't have any doubts, and personally I never met anyone that was truly happy in this cult. What keeps them in is the fact that they are trapped in, in one way or another. It’s not that they enjoy being enslaved as this rabbi seems to believe.