It took them by surprise because a lot of engineers/designers tend to overlook the obvious and simple and like to deal with the most complicated aspects and assumptions they can come up instead with their designs. To be fair, who would really think that a plastic cap could open up the cyclindrical locks? Most people would test locks with picks and the other usual tools of the crooks which I guess, mostly did not work on the cylindrical locks.
On the other hand, the first guy who picked the cylindrical locks successfully with a BIC cap might have just stumbled into it when he/she was fumbling/fidgeting around with a lock and a pen cap.....then suddenly, to his/her surprise,.........the lock opened.....

Chombi