It's an urban area, but there are several post offices within a mile of downtown. It would probably make sense for the private sector to supply post boxes. It really isn't necessary to have a full blown post office when all that's really needed are store fronts with PO boxes. The USPS made a big stink when private companies started trying to provide mail boxes, and they wouldn't let them be called PO boxes in their addresses. They are called Private Mail Boxes (PMB). This foolishness should be ended.
Remember, USPS does the distribution, so when they have a PO Box to deliver to (in an urban city delivery area) the mail addressed to the box is separated from the mail addressed to the street address.
A box customer turns into two addresses, and creates new distribution costs to handle the mail.
The private mail receiving agent typically charges MUCH more for a box address than USPS.