The Watchtower religion works hard to instill a concept that is hard to dispel. They begin by demonizing all entities and organizations outside their own, and creating a society of persons reliant on them for guidance as to how to dwell within society without 'touching the unclean thing'.
They then elevate themselves [the GB and those in charge] as beyond scutiny. Thus the organization takes on a lifelike persona of it's own in the minds of believers. The 'shotgun' style of scriptural proofs presented to keep the flock convinced of the doctrines gets rarely questioned as most witnesses have little education in the languages and culture of the Bible.
Once the concept that God has selected them as 'his special property' is deeply embedded, particulary by use of factual misrepresentations and historical inaccuracies, and percieved 'persecutions' arise due to family opposition to one's joining the group, the hook is set.
From then on any questions are condemned as 'heresy' and 'failure to wait on Jehovah' to act. The isolationism that has been promoted works to keep even those disbarred ones from feeling freedom to investigate closely.
Additionally, the FS is a big tool in this - a witness is constantly fending off logical arguments against them possessing 'Absolute truth'. This makes good practice when one has doubts, and such doubts get routinely pushed aside as 'dangerous thinking', and dismissed, or at least shelved for years, even decades.
I was among those who shoved doubts away for decades - I do not consider myself of grand intelligence, but I am no one's dummy either. I was a captive to strong indoctrination and mind control tactics used by them.
Jeff