> That isn't the case at all in my experience. In any neighborhood I've ever lived in, you see at least one van from each organization come through daily. And if anything, UPS and FedEx come through more than once per day sometimes, whereas USPS doesn't.

USPS doesn't deliver freight, UPS does. So yeah, you are going to see both in a residential setting but you won't see any USPS trucks making freight deliveries in an industrial area. UPS has to support that use case, USPS doesn't.