You have the basics correct, but not where they make the profit from. Someone spending $3,000/month on a card and paying it off winds up paying little to no int

You have the basics correct, but not where they make the profit from. Someone spending $3,000/month on a card and paying it off winds up paying little to no interest. However, they do get to make a good deal off of the fees. Like the article says, the fees make the cards a lot of money. That person putting $500 per month on the card likely isn't poor either unless they are paying most of their expenses with it and paying the card off each month. Again, they get some fees. With a limit high enough for $500 a month without paying it off, they aren't as high risk - after all, that is at least a $6,000 limit. That's a full 20% of a 30k/year income, after all. These folks are in a middle ground. The company can make some of their money off of transaction fees, but will try to make up for it through interest rates, which won't be all that horrible. The actual poor person has a credit limit of $500-$1000. They aren't spending enough for the company to make much from fees, so they try to make it up in interest.