I would ponder a guess that because they have to rely so heavily on WTBS publications to understand the bible, no real understanding can happen.
I also think the WTBS has a habit of kindergarten school all in the Bible, therefore it makes it extremely difficult for those who want more than a superficial knowledge - they have to do that pretty much all on their own.
So, when confronted, most (like me) couldn't defend their faith adequately if their life depended on it. If they stop talking about a certain topic, its because they have to go home to "research" as they don't have all their volumes of WTBS literature with them for index referencing.