Huh? Why? Isn't the USPS a mail company? I don't get what that has to do with banking.
There’s no other department of the federal government with that coverage.
They also are quasi financial already as you can get a USPS money order.
It could also be pressure on American banks to treat their customers better, since the USPS is not burdened with a responsibility to generate dividends for shareholders.
The USPS is also not directly funded by taxes (though it is indirectly subsidized via it's tax status and sole right of access to mailboxes), and with the waning popularity of letter mail, would become more self sufficient in the long term if it branched out into other services
Other countries also combine banking and postal branches for similar reasons, like Japan (although it is in the process of being privatized).
On the flipside, they are one of the most ubiquitous ATMs in Japan and your local post office will double as a branch for JP Post Bank (which are everywhere).
Oh and it's nation wide too! Which is kind of important for a country where some banks restrict activities and branches to their direct locality.
Man. I wish patio11 would talk about Japanese banking more because to most American audiences that system is also just, completely something else.