I happened to come across a Time article in 2008. It was basically talking about the high turnover in American faiths. It mentioned the jdubs and highlighted the following point.
An even more extreme example of what might be called "masked churn" is the relatively tiny Jehovah's Witnesses, with a turnover rate of about two-thirds. That means that two-thirds of the people who told Pew they were raised Jehovah's Witnesses no longer are — yet the group attracts roughly the same number of converts. Notes Lugo, "No wonder they have to keep on knocking on doors."
Throughout my years as a witness, I have personally seen people come and go. The retention rate appears to be quite poor and not that many converts in the congregations I went to. I have seen quite a few people fade and disappear without a whisper of why? Some left because they didn't get on with the elders. One young lad left because he had a 'worldly' girlfriend. And another guy left because he didn't feel good enough!
Is this something you have experienced?