Interest rates are the lowest they have been in decades, but credit card users have yet to see the benefits, even while banks are increasing their card profits, Fortune reports.

In the four years since the Federal Reserve began a bond-buying spree, credit card rates have actually gone up, reaching an average of 12.06 percent in May, compared with 11.94 percent before the financial crisis began, according to data from credit tracking firm Cardhub cited by Fortune.

“Why haven’t credit card companies passed along the savings?” asks Kathleen Day of the Center for Responsible Lending. “We think regulators should look into it.”

Editor's Note: Prophetic Economist Warns: “It’s Curtains for America.” See Evidence.

For instance, in the most recent quarter, loans made by Capital One Financial, which earns about half of its revenue from credit cards, generated nearly $4 billion in interest income, $900 million more than a year ago, when interest rates were higher, and the most the company has ever made in any quarter in its history.

Fortune says it is unclear why card rates have not declined, but industry experts say borrowing is only one of the costs these companies have to pay.

One factor obscuring the rate environment might be the Credit Card Accountability Responsibility and Disclosure (CARD) Act, which was passed in 2009 and makes it harder for banks to charge card customers hidden fees.

“It’s a real 12 percent, instead of a fake 6 percent that really turns out to be 32 percent when you add in all the fees,” Ed Mierzwinski, head of consumer issues at Public Interest Research Center, tells Fortune.

A Capital One spokeswoman says its rates are in line with competitors, and notes that interest income is up in part because of acquisitions.

Meanwhile, at Citigroup, the net credit margin for its bankcards is up 24 percent in the past year.

Lack of competition could be a major factor why credit card rates have remained high. The top seven card issuers now control nearly three-quarters of the market, up from 60 percent a decade ago.

“Less competition means less price pressure,” Jeff Harte, a bank analyst at Sandler O’Neill, tells Fortune.

Greg McBride, senior financial analyst at Bankrate.com, says to look to Congress for why credit card rates remain high.

The CARD Act prevents issuers from raising rates on an existing balance until the cardholder misses payments for more than 60 days. To make up for that, issuers are just hiking rates up front on all cardholders.

"The overriding factor in that increase in rates is [the law]," McBride says.

"That’s like telling an auto insurance company that they can only raise the premiums after the car gets totaled. If somebody’s getting speeding tickets and DUIs, there’s a lot of risk there."

Editor's Note: Prophetic Economist Warns: “It’s Curtains for America.” See Evidence.