It is a government agency, despite the legal fiction that it is not. It is run by ruling elite that thinks that it deserves special privileges while it looks down its nose at the ordinary people.
Certainly never noticed that ~ it does have too many alcoholics at the top ~ typical of so terribly many industries, but in general it is recognized that the American people OWN USPS and that none of them are any more deserving of favor than anyone else ~ hence the kvetching all the time. Some people want to think of themselves as exclusive owners.