Businesses are charged about 2-3% per transaction for credit card fees. If you're doing significant business, this can total be a ton. For example, in terms of percentage of income, our business in january of this year had 10000 dollars in credit card fees. Assuming a standard 1.3% interchange and assessment fees (the one going to the card issuer) that means they took home at least 2K in fees. It's probably closer to 3, but at least 2K in fees. THat's one business in our slower months. If we do it on the year it's at least 35K (that's not factoring the per swipe charge of a nickel per swipe) that's from a single small-med business.
That's of course not factoring in interest paid by the customer as well.
According to Visa they had 16B in revenue from "Data Processing revenues" the biggest piece of their revenue pie. \
Trust me these credit card companies aren't hurting.
You have absolutely no clue the amount of overhead that is included in processing and settling credit card transactions.
Hint: I worked in the finance department for a publically traded acquirer/processor.