By getting into a credit card contract, you effectively obtain a revolving credit limit, essentially a loan that once paid is again available (in contrast, under a debit card contract you only get the facilitation of "plastic money/carry no cash", but you are contractually obliged to fully pay the balance on the date due. Diner's Club, the first card, was and remained for decades, such a "debit" card).
Now, people don't just "forget" to pay the credit card on time in order to not incur interest costs: they may purposefully leave some amount unpaid, in order to smooth their consumption patterns, effectively using the credit card as a loan facility to do that. What? With the usual "exorbitant" interest rates credit cards charge?
Well, if you cannot get any other kind of credit, you take what you can get, if you really need it, or want it.
So the bank looks at:
1) The fees that collects from the supplier
2) Handsome interest income from customers leaving some amount of the utility bills unpaid, turning it into a loan
3) If they are new customers, lured from the "bills payment" ad, that they will use the credit available to make other purchases also, so more fees and more interest income.