You have hit on the EXACT reason that the USPS is so critical. There are huge areas of the US which are not serviced by other private delivery services. And even in areas where those services do reach, I imagine the cost is extremely high.

People in Barrow, Alaska deserve access to mailing services as much as people in NYC. Without that, there is no reliable way to contact everyone in the US for the purpose of the Census, Voting (where mail-in voting is available), Jury Duty notifications, Selective Service, etc.

There are critical government services that still must be run over "snail mail" and to pass that off to a private institution which will not be able to service all areas equally will lead to more inequality.

Not only is it valuable to private citizens, but FedEx and UPS use the postal service for last mile delivery as well. For example here's FedEx:

https://www.fedex.com/en-us/shipping/fedex-smartpost/network...