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.
Per your earlier point about freight I can imagine that UPS/FedEx have a lower percentage of company traffic in residential areas than USPS does. But I find it difficult to imagine that the total number of trips to residential areas is lower for them. They simply have more non-residential traffic than USPS, not less residential traffic.