Banks may consider many balance-carrying CC customers as "good" customers, but they likely also consider high-spenders who pay their bills in full every months "good" customers.

The issuing banks earn money -- in some cases 3% -- of every transaction. If I spend $10K/monthly and pay it off in full, the bank still earns something over $3000 per year on my account. And the risk of a defaulted creditee is not there in my case for the bank.