One elder explained to me the reason he stays in is because he believes the 1914 maths. Sadly he is being conned but in an extremely clever way. It is the numbers that are being fiddled with. WT provides convincing answers to some of the anomalies. Academics do the same thing but come up with a different date - but it's a similar trick whether within a secular/academic frame or a WT frame.
Why do intelligent people make wrong decisions about work, housing, investments, child rearing, whatever? Everyone makes mistakes. Some are more serious than others. Does everyone correct or do they double down on their mistakes?
People have powers of reason. In relation to the Watchtower, when wrong information is broadcast/published, why do people who can reason it out go along with a falsehood? Sometimes it is a coping mechanism because they are in a very difficult situation and they don't know the Bible very well.
Yes, they hold on to a set of superstitious beliefs. But so do a lot of other people in all walks of life.They should all know better but it's not like that. Crafty lies are powerful things.