In the case of CC they get the merchant fee. If they can get the merchant to switch from taking cash to accepting cards they get fees for using a card vs no fees for when the customer uses cash.
A couple of percent on all of the retailers' turnover is a good incentive for a CC company to accept anyone who is willing to use their cards.
More possibly to do with covid and the lockdown a few of the small businesses close to me have gone from cash only (no £50 notes accepted*) to also taking cards and judging from what I've seen a lot of customer do use cards for every purchase. During the two years of Covid restrictions I only used around £100 in cash - the rest was by CC card.
Cash flow. The CC company still have to pay the retailer in full, possibly within 60 days or less. How do they do that if all their customers take years to pay off what they have spent? They rely on customers who pay of 100% of their CC spend each month.
But if the default rate is high the interest rate only covers the amounts they have to write off - but not the money they have to pay back to the retailer in a timely manner.
- A couple of years back I saw some convincing plastic £10 note forgeries and recently a couple of shops close to me have recently put up notices saying no £20 and £50 notes.