I still think they make enough cash on me through the credit card processing fees to make me a profitable customer.
You also need to take into account the bank's cost of funds, the cost of administering the account, the cost of fraud, cost of disputes (do you ever do a chargeback?)
The marginal cost of servicing another person when they already have a consumer base of people with debt is very small (close to zero). I'm trying to say it's still profitable, but not where they make the bulk of the revenue.