They are trying to create a disincentive for behavior that they want to discourage. It has nothing to do with what (you think) their costs are.

They could say "We are no longer accepting credit cards for payment. This would obviously outrage a large portion of their customer base. What they are saying instead, is "we don't want you to pay with a credit card, but if you are willing to pay enough extra every month, we will put up with it."

When I was young I worked in an automotive machine shop for several years. There were maybe 4 or 5 other shops in town and we were all friendly-competitive. If a job came in that we didn't have the time/space/equipment/interest in doing, we would farm it out to someone, and they would send us the stuff that they didn't want to do.

Most of what we did was repairing engine components. We would rebuild your cylinder heads, grind your crankshaft, clean your block and install bearings, etc. Sometimes, people would disassemble the engine themselves but bring us all of the pieces. We would clean everything and return the engine fully assembled. We probably charged $125 (in 1985 money) to fully assemble the engine.

One of my good friends owned one of the other shops. Sometimes my boss would loan me out to him, so I spent a fair amount of time in his shop. One day, a customer came in to drop off some work. It was most likely a standard small block Chevy v8 (or Ford, or Dodge, something like that). As they were wrapping up the negotiating, the customer asked how much it would add to his cost to have the engine assembled.

$750 was the reply. The customer declined, he was suddenly willing to put it together himself.

After he left, I asked my friend how he got away with charging so much. He said that he *hated* building engines and didn't want to do it - but somehow the hate went away when it was putting $750 in his pocket