The way I understand it, a certificate of deposit is a very simple, variable-term investment directly in a bank; its yields are relatively low but it's something you can have quite a lot of confidence in... in a legitimate system. The problem arises with a fraudulent system; it is impossible to gauge your risk when the bank in which you wish to invest is just as overleveraged as it is unaware -- at least until the point they become aware and try to sell off everything to cover up their mistakes.
Those CDs, which would be as golden as bonds in a legitimate system, instead are the alarm that something is very wrong, to me.