They don't have to.
With the explanation or changed viewpoint of the generation in 1995, there is no need to change since it allows for an indefinite time
for this system to go on.
The majority of the witnesses do not stop and meditate on what they are being fed by the GB.
They truly beleive they are used and directed by Jehovah and they can do no wrong.
Look at the changes they have made in the blood doctrine, very few understand it, most are willing to take all the fractions of blood allowed,
if they would only stop and think, they would realize it's nothing but a joke but they blindly obey like zombies.