I think that when a long held faith falls apart, especially a faith like the JW belief, it is a natural process to go back over all that you have ever been taught with a fine tooth comb.
You come at it more objectively, are more honest and this goes onto highlight the flaws in the belief and the delusion you have been under.
The undermining aspect of this inclines people to do a thorough research of what they have been involved in, largely because of the need of healing.
As a result they become encyclopedic on the subject and therefore know more than people still involved in the faith.
This then has the knock on effect with regards to the entire subject of belief. When you see through one you tend to see through them all.