Why do you think they do?
It's not a choice....they have no....American are too (fill in the blank: distracted, apathetic, entertained, cynical) to get politically involved and demand re-institution of usury laws to put an end to exorbitant credit card interest....
Why would Americans want to get directly involved with things that really matter??? Such matters are trivial when you have celebrity sex scandals and little boys floating away in runway balloons to concern yourself with. Just let the banks and big business do whatever they want.
They feel obligated because they are legally obligated. They agree to pay the ridiculous interest when they use the card. That is the cost of spending somebody else money
I don't - I pay mine off every month, so don't get charged interest.