The Stumbler, JWs at their core, are not pure lovers of truth - maybe they were when they were first introduced to the religion, but they morph into something else with time. JWs at their core, are first and foremost, loyal followers of the organization. They value loyalty to the organization above actual truth. You wanna know why that is?
Because they have been mentally and emotionally ensnared with the concept that their organization is "Jehovah's Organization" and their body of leaders is "the Faithful and Discreet Slave". They believe they must be loyal to "Jehovah's Organization" and accept whatever "the Faithful and Discreet Slave" teaches in order to have Jehovah's favor and survive Armageddon.
With their minds infected with this propaganda, truth becomes a secondary issue. "The Truth" is not so much about what is true as much as it is about loyal association with the Watchtower organization. So any time you point out any error in the organization's teachings, you are perceived as attempting to erode their loyalty to the organization. It doesn't matter if what you're saying is true and the Watchtower is wrong.
To a JW it doesn't matter if the Watchtower is wrong about anything or lied about anything because "they're just imperfect men" and "the light gets brighter" and it's still The Truth because Jehovah chose them in 1919! They have been fed cliche excuses for being in error, but they are conditioned to believe that they must not under any circumstances be disloyal to the organization - and to them, simply acknowledging that a current teaching is wrong, amounts to disloyalty.
Because disloyalty to the organization equals disloyalty to Jehovah which equals no paradise earth for them. So it all boils back down to fear of losing out. It is this fear that motivates them to be loyal to the organization at all costs - even at the expense of turning a blind eye to the real truth. Loyalty to Watchtower "truth" is more important than loyalty to actual truth because they think it is loyalty to Watchtower that will get them into paradise.
JWs are really followers of a group of men - the governing body - who hide their profane authoritarian leadership over them under the cloak of "Jehovah's Organization". It goes down more palatably to say "obey Jehovah's Organization to have Jehovah's favor", rather than to say: "obey Samuel Herd, Anthony Morris III, Guy Pierce, etc to have Jehovah's favor". The latter statement sounds cult-like, but ultimately it's the naked ugly truth being covered over by the former statement.
JWs obey the ever changing teachings of these men as doctrines. The teachings of these men is the ultimate focus of the beliefs of JWs - not the bible. They only make secondary use of the bible to proof-text these men's beliefs, according to how the men teach them to twist the scriptures to support them. So the bible is really not their ultimate authority or their ultimate focus of attention. Watchtower literature is. What JWs call a "Bible study" is really a study of Watchtower literature and Watchtower teachings.