While I agree that the FDIC will bail out depositors—even above the 250K limit as we have seen in the past year—there is a risk for bank stock (equity) holders.
That is the basis for the lower rating.
Most banks are technically insolvent if they had to liquidate everything immediately. In fact many have commercial real estate liability alone that substantially exceeds their total equity.
Agree...Commercial real estate loans are the powder kegs under the security of many banks.