From Clark Howard show notes
Basically, the big banks want to put their low-profitability customers into a penalty box of high fees and red lights. And when I say red lights, I mean that almost literally. When you call up a giant bank, a color typically pops on the customer no service rep's screen that lets them know if they should help you or not, based on how much profit you represent to them.
They won't help you if you're not in the "green," both on the screen and in your finances. You need to have north of $50,000 in a checking account to be considered a profitable customer.
For a typical checking account at the big banks, the interest rate is probably under 0.10%. So I can see how profitable these checking accounts can be for the banks even if these customers avoid fees.