Every time you charge at a merchant the bank earns a fee. A person who charges steadely generates income to the bank. A person who has a long consistent record of paying on time is usually a minimal credit risk. Result from the banks perspective, income a minimal risk.
I had a client who was generating $15K overdraft fees on his checking account. Obviously a very profitable account for the bank. However, they closed his checking account and terminated his relationship with the bank. Reason, profitable yes, but perceived risk was high.