With the proliferation of "free checking" without so much as a minimum balance in most cases banks have essentially created a selection system to continually marginalize customers that aren't profitable while selecting for customers that are.
From the standpoint of a business (which banks are) this is understandable. However as has been noted in other comments banks also serve a utility function and for the the type of customer that routinely doesn't have $2.50 in their checking account to trigger that overdraft in the first place several hundred dollars in fees might as well be a million. Of course they take off and the account gets closed. Now, because of a $2.50 loss to a bank, they're essentially excluded from the most basic functions of the financial system while people like us continue to benefit from free products, preferred interest rates, credit card points, etc.
Simultaneously, if due to some perfect storm of events (cash flow, mistakes, etc) if customers more similar to us somehow end up in this situation we'll pay the fees. The bank has a "valid" reason to boot the poor, they make a ton from the middle-ish class, and they stay in good favor with those of us that are more wealthy. They can't lose.
The extremely simple (but overall less profitable solution) is to just decline the charge.
My preferred status at banks is being subsidized by the poor and that doesn't sit right with me. I've tried credit unions but they're almost completely unable to meet my needs.
They want customers they can extract usurious and otherwise abusive fees from. They don't want the subset of those that will fight back against said abuse, which is what they use ChexSystems for. The latter also randomly hits some people from the (rest of the) former group, but not enough of them to impact the bank's finances.
Wait, so which one is it? Do banks want to exclude people with overdrafts because they're bad customers (for whatever reason) or do they want those people because they can rake in the overdraft fees?