I was speculating to my husband recently on the reasons for the dire financial straits of the United States Postal Service. Well, the Internet, of course, but the alternative delivery services seem to be doing fine in the same environment. Why is it different to be UPS than the USPS?
And then it dawned on me: the Postal Service has a mandate to deliver mail to every person in the United States. That means a Post Office and a Postmaster and probably a Mail Carrier in every small town. Other delivery services can focus on profitable markets and let small-town customers make the drive to the nearest big town if they want to use their service.
Pure speculation, of course -- my specialty. So I was extremely gratified to read this analysis which draws the same conclusion (and points to an outline of some other significant factors).
Update: Here's an Economist article that makes many of the same points.