[leoc]

I'm not well versed on the subject, but I assume it was just another of those large-scale intelligence failures, like the https://en.wikipedia.org/wiki/Englandspiel only with the boot on the other foot. Groupthink in action again. Also, given the large number of important ciphers which were broken during the war, I'd guess wildly that the pre-war crypto communities (such as they were) were generally much too complacent about the risks from cryptanalysis, likely because ciphers had never been subjected to state attack on a Manhattan Project scale before. Comparable to the long time it apparently took for people to become generally aware of C buffer overflows as a serious security problem, maybe.