Check out this picture. This is at a U.S. Post Office. It was the only machine in the place:
So this post office has PO boxes. There are mail slots to drop off mail. But, sorry, you can't buy stamps at this post office. At least off hours. If during "business hours" then you can wait in line and get one from a real person.
Who thought of this? Does the Post Office think that if you go to a real person the next day that will produce savings for the government? If they have done anything at all they shifted costs to the consumer - you have to spend extra time and effort to find and get stamps, and the government won't have to pay somebody to spend 30 minutes filling the machine every day.
Do we want these same people running our health care system?