Charging a "dormant account" fee seems like a banking practice from the 1950's, but local banks still do it. If an account has a balance large enough to allow free checking, why do banks charge for dormant accounts? I'm sure the answer is that it is profitable for them to do so, but what are the economics of this?
Banks get exhorbitant fees (relative to their expenses) when they sell you books of checks for your account. So perhaps the loss in revenue from not selling printed checks makes them want to discourage dormant accounts.
Another theory is that banks can make money on the accounts of people who die. If an estate is not settled quickly, the bank accounts of the deceased could be dormant.
Another theory is that banks want people to put their money in certificates of deposit with the bank instead of leaving it in an account.