Yes, it’s a real thing. When I worked at a major bank the customers that would pay in full monthly on their cards were considered the “bad” customers. Those that paid only minimum and got hit with late fees were our “good” customers.
From their perspective, they make nothing off of people who don’t pay interest or fees. Thus, it only makes sense that the “best” customers are the ones carrying a balance, because they’re the ones who generate profits.
They still make a percentage of each transaction. But it sure isn’t 18% interest