Lots of credit cards come with incentives. For example, I get reimbursed a flat 2% rate on all transactions ("cashback"). As long as I keep the card on auto-pay

Lots of credit cards come with incentives. For example, I get reimbursed a flat 2% rate on all transactions ("cashback"). As long as I keep the card on auto-pay for the full balance, it's a win-win situation: credit building + free money. Where does that "free" money come from? From the payment network fees, of course. Mastercard takes a 4%-ish cut, the bank keeps 3% of that, and 2% of that goes back in my pocket. Banks have to offer such benefits because they will get cannibalized by the other players if their card can't compete. Structurally, it's actually quite stupid that there's an invisible tax which you can only recover by playing ball with the creditors... but on an individual level you would have to be foolish to not take advantage.