Earlier quoted context omitted.
Most interaction with USPS is at (residential) mailboxes. Sure, post office service is not great but they do a decent job of moving letters, post cards, and packages in a relatively timely manner - and the service for letters and postcards is damn cheap. In now remote / rural areas of the US, no for profit company would bother providing service, as it is wouldn't be profitably - but USPS serves everyone.
It's "damn cheap" because it's being subsidized heavily by US taxpayers. "The United States Postal Service (USPS) on Wednesday reported a net loss of $4.9 billion for the year ending Sept. 30."
https://en.m.wikipedia.org/wiki/Postal_Accountability_and_En...