Opportunity cost, the banks in no way payed out what that money was worth at the time. Hand me 1 billion interest free for 5 years and sure I will pay the money back, but...
As that points out, not all loans where paid back. The interest from those that did result in a nominal profit, but it’s far from what private lenders received for loans in that time period.
Thus opportunity cost, as it was a poor investment which is why it was called a bailout.