FDIC insurance covers $250k, which is basically 0% of billions of dollars. Storing money safely is a hard problem. Cash in a vault has negative interest (due to

FDIC insurance covers $250k, which is basically 0% of billions of dollars. Storing money safely is a hard problem. Cash in a vault has negative interest (due to the overhead cost) and a lot of risk, a balance in an FDIC insured bank also has risk, if the overhead cost of T-Bills is tiny then it's a preferred method. What you're looking at here more than anything is a big vote of no confidence in the stability of the big banks.