So I worked in Retail Fuels for quite a while and have a little understanding of CC use. Here is sorta how it works, you sell something and want to let people use Credit Cards. You cut a deal with Visa, Master Card, etc. They will in turn charge you for people to use it. Typically this comes in the form of a swipe fee (can range from 15 to 28 cents) for every use, and a percentage charge (runs from 2 to 3 percent) In other words Banks and Financial Institutes make pretty darn good money for processing credit card transactions. Now in the new world there are a lot more ways to pay, Pay Pal, Apple Pay, Debit Cards etc. So more and more companies are trying to get a piece of the action. Think about it, in my world of Retail Fueling if we process all the CC transactions for all of 10,000 stations and they average 100K gallons a month at say $3 a gallon. Daily average sales of 3,333 gallons per station. That is about $100 million a day. Not to mention all the Ho Ho's and Twinkies, tobacco and everything else they sell. Three percent is $3 million a day for processing credit cards. Now think about how much money is paid for all the purchases made across the country everyday.
So the moral of this story is that if you get a discount via a particular credit card then you have to use the credit card. In other words, when you ultimately pay for whatever you bought with real US currency, the people you are paying needs to be the credit card issuer that gave you the discount or you don't get the discount. They have no reason to give the discount otherwise. Also the cost of these discounts are usually shared by the credit card issuer and the merchant or store giving the discount.
