The United States Postal Service has been prohibited by law from giving discounts to large shippers which puts them at a disadvantage to UPS, Fedex and other private shippers. There's talk of changing that prohibition. By law, only the Postal Service can handle letters. OTOH, the postal service is required to deliver at the same rate to everywhere in the U.S. and its territories.
Nothing said about the USPS applies to any other country, or probably any other business in the world.
Until about 40 years ago, the Post Office was run by a "general" of sorts, the Postmaster General, appointed by the president, who was a cabinet member. (our foreign policy and defense were run by "secretaries" LOL}
Our U.S. Postal Service is doing better in recent years but it is still a huge money loser. Our mail does get through. I've found delivery to be about as reliable as UPS, but the level of service is somewhat less.