Experts blame the improving economy: Consumers are feeling more confident in their overall financial situations and they’re loosening their purse strings because of it. That confidence led to higher retail sales through the holiday season, but the credit card bills are coming due, and people are leaving them unpaid at an alarming rate, according to S&P and Experian. Another factor in the uptick in default rates is the increased willingness of financial institutions to extend credit to those who may struggle to pay it back.