Skimmer, I think that the change in the generation doctrine has given people doubts. I never did believe what they wrote about that, but I thought that that would be put right. I suppose I still believed that Jehovah would clean up his people, starting at the top.
Also, I thought that there had to be a true religion, and believed that the JWs were the closest thing to the truth. I have recently realised that that was because of the resurrection hope. I wanted that to be true, so let myself be partially blinded.
However, I slowed down. I withdrew from the school, started missing meetings regularly, became irregular in FS, then inactive, then finally decided to leave.
I know there are others with doubts still active, mostly for family reasons. So there may well be a constant trickle away from the JWs.
esther