Could you elaborate on that?
For example, if you spend $500 a month with your credit card but you pay every balance before it has a chance to collect interest then the issuing bank will still make something like $100 a year off of your purchases (give or take). This obviously pales in comparison to the 10x more revenue they could make if you never paid down your balance and racked up lots of interest, but it's not exactly nothing.
Also worth remembering is that high balances and high interest payments are higher risk (if we'd forgotten this from the recent/ongoing financial crises).
Also, I'm pretty sure the merchant bank gets a significant portion of the fee.
But, cards that offer cash back can eliminate this. So they only make money off of interest and late fees.