I question whether the interest is worth more than the merchant fees they get from wealthy people using the card constantly. If one poor person is paying, say,

I question whether the interest is worth more than the merchant fees they get from wealthy people using the card constantly. If one poor person is paying, say, 11% interest on their $500 balance for a year, then the company makes a few hundred bucks on the interest. If a wealthier person spends $50k (admittedly random number I made up, its going to vary vastly for different card-holders, and probably in the millions for many) with their card over the course of the year but pays it all off immediately, they've made between 1k and 1.5k risk-free on the 2-3% merchant fees, and the customer will probably continue to use that card.