What I heard was they let the "anxieties of life and materialism" weigh them down and distract them. We were always told that our spirituality is kept strong by adversity and that comfort and prosperity were "our" test and it could be the undoing of all of us here in the U.S.
Had these Germans not been JW's they likely would never have been imprisioned. Once they were locked up in there, it didn't matter if they renounced their faith or stayed faithful, they were stuck and had no choice but to do all they could to survive. How disilliusioning it must have been to survive through that Hell, only to come of it and find out it wasn't even the great tribulation at all and also to realize that the leaders of the religion hadn't suffered one bit. These survivors had to start all over again and their old friend, the carrot of the New System was still there being dangled in front of them but only after the real great trubulation came first.