Yeah, it's not animosity it's just capitalism being... callous.
Mail is recognized as a necessity so the US Post Service has to deliver it to literally every address in the country, including the Alaskan boonies, at whatever cost. It's a burden, but it's the nature of the Service.
Private delivery companies like FedEx, DHL, or the semi-infringingly named UPS (I experienced brand confusion for a LONG time) don't have that requirement. I've heard that if they need to deliver something to a rural American then they'll often use the USPS for the worst parts of the journey.
That's not animosity, it's just capitalism being... callous. Again. What's beautiful to me is that the USPS remains a very competitive "company" despite having to provide such services. We pay incredible overhead to these private corporations for package delivery and what do we get? Sub-contracting the worst jobs to the public service who's legally obligated to do the hard work. Brilliant stuff.
I'm not going to go full socialist here, but I think there are some services which might benefit from "capitalist efficiency" and some which absolutely do not. Insurance of any sort should never be private, and utilities probably shouldn't either. Competition doesn't lead to better outcomes for such necessities, it results in wrongfully denied claims and service losses. I don't know if banks can benefit from competition or not, but I know that they sure robbed us blind with collusion in the Banking Crisis.