In regards to ThatRobGuy's post (referenced this way rather than quote the same thing; credit card companies and others have traditionally turned to fees for steady revenue. It's a practice so old that variations were, IIRC, used in the late Medieval period to get around the Church prohibition against usury. So if a credit card company, through shear chance, had every one of their customers pay off their balance every month, they could turn to fees to at least keep going. Some IIRC, charge both fees and interest.
They might not base all their interest rates on risk, but risk is definitely a factor. They might not be able to "skip out" on debt but they can declare bankruptcy. That, BTW, isn't the universal panacea some think it is, but it still makes it difficult or outright impossible to recover debt. It's incredibly easy to run up a large credit card debt before you know it, whether it's for an emergency or not keeping up with spending. Have experienced the former and have seen people get in deep with the latter. And, as we all know (or I hope we all know), credit cards make for very expensive loans.
What credit card companies seem to want is for people to keep at least some balance. "Earn money back," or incentives to use them for household expenses, the better to run up a balance you can't clear in a month. They're not going to pay back more interest than they earn, so if you don't pay it off every month, it's not any help.
At best, the goal should be to pay off the debt and then pay off future credit card debt every month. Low interest would be welcome, and if interest were capped and I had a credit card debt, I'd try to take advantage of the cap and pay it off. Given human nature, that's not likely to happen, particularly if a credit card is almost maxed out.