They're creating new "money of zero maturity". If I have a CD I can't withdraw for one year, and that's used to create a loan due in one year, that's one thing. The problem is when money in my checking account that I can withdraw at any time, is used to make loans that can't be called in at any time. This is what creates the possibility of a run on the bank. Banks borrow short and lend long, which is profitable, but can with some justice be called fraud.