So to the extent that banks have deposits, they can’t lend them out in the quantity they used to (or aren’t because of tightened credit policies). Instead, they buy Treasury bills, according to Bill Hampel, the chief economist for the Credit Union National Association. And those don’t pay as they once did because of the interest rate environment. Nor do they deliver the kind of returns the banks would get if they were lending the money under normal conditions.

The resulting lower profits make it harder to raise the rates that savers earn. Meanwhile, lingering losses from loans pose their own enormous pressures.

THE REALITY OF THE FED If money is so cheap, why can’t financial institutions give us a bit more? After all, banks can just get money from the Federal Reserve and pay close to nothing for the privilege.

Well, at least in theory they can, but only so much and only for so long. “You don’t really want to borrow money like that if you’re a bank,” said Dan O’Malley, who runs PerkStreet, which sets up customers in a checking account with a debit card that can pay back 2 percent in rebates. “It looks bad to regulators, like you didn’t have enough deposits to plan your business well.”

While PerkStreet has been extremely aggressive with its debit card rewards, it does not plan to top the interest rate tables when it introduces a savings account next year. “I don’t think it’s sustainable,” said Mr. O’Malley, who noted that many banks that once topped the charts now pay much less, while crossing their fingers that customers won’t leave in anger. “We don’t want to pump and dump.”

THE F.D.I.C. RATE POLICE Last year, I wrote about the curious case of Ally Bank. Its troubled parent was the recipient of federal bailout funds, and competitors successfully persuaded the Federal Deposit Insurance Corporation to pressure Ally to lower the rates it was paying to consumers.