Over the past few decades, the credit-card market has quietly transformed into two credit-card markets: one offering generous benefits to wealthy Americans, the other offering expensive debt to the poor, with the latter subsidizing the former.

In the credit-card industry, the well-to-do are known as transactors. They pay off their balance in full every month, avoiding late fees and interest charges. They use credit cards as a convenient payment method, and as a way to earn travel points, cash back, airport-lounge vouchers, seat upgrades, and other goodies.

In contrast, the have-nots are known as revolvers. Revolvers are subprime borrowers who use credit cards as a payment tool and as a short-term loan, to cover surprise expenses and groceries the week before payday. Such customers tend to take out no-frills cards, without lavish cash-back rewards and travel points. They also tend to carry a balance from month to month, and sometimes from month to month to month to month.