Brilliant move on the banks/retailers side.
Get the sale, minimal risk considering the actual cost of many things. And if they don’t pay, the debt collectors are right there.
Lets face it, people are more likely to pay $20 a month than save it and budget the purchase.
And with retail sales stagnating for a while, any sales are good, especially when the person is going to be buying other stuff at the same time. Get them in the door, keep them coming back.