Don't forget that each of the Governing Body was indoctrinated for decades prior to reaching that position. They honestly believe it to be the truth, and that they are benefiting people.
It is possible that some of the current GB have come to realise they are not directed by Jehovah (as occurred to R. Franz). However, it is a very difficult thing to leave. The GB have one of the powerful roles on earth (amongst their peers). They have accomodation, meals and cleaners and chauffers provided. They travel the globe. They are looked up to as the very hand of God, his direct spokesmen, receiving what borders on idolatry from many JW's. Imagine at the age of 60+, with no education, no "worldly" friends and no financial backing leaving that and starting a new life.