1) Cable companies would prefer to not provide cable to all people in a state, only providing cable to those who will buy premium services and in highest concentration areas so it's most profitable, but states general have laws stating "no, cable for everyone or you ain't in business." So the USPS should not provide mail service to absolutely everyone in the US?
2) One stamp for 44 cents seems insane, but it adds up over time. Small businesses have had to mail as well. Only recently with the maturity of free mail services and bulk email programs does this no longer make sense for letters but for larger parcels it still creates economies of scale for shipping businesses.
3) A few minor businesses like, oh I dunno, Amazon, benefit from ubiquitous and cheap shipping provided by the USPS so the subsidation of cheap mail rates and others can be argued stimulates online commerce. It was never a complaint by Sears back in the day.
4) The USPS actually is a government-mandated service that delivers flat-rate mail to every corner of the country six days a week, and there's no reason to create a false dichotomy that it absolutely has to be subsidized. The USPS worked just like this for decades, because the internet did not exist. The internet is a disruptive technology. On one hand, millions of people still need snail mail. On the other, the USPS needs major changes to continue to exist.
The main reason for the massive news upheaval is simply because it's going to be a political third rail. Simply put, drastic changes need to be allowed, but to do so would put every congresscritter, Democrat and Republican, in hot water because it probably means raising rates, cutting jobs and pensions, or both. The political will, like on so many other issues, is nowhere near there yet. It affects too many re-election bids.
Unfortunately, changes need to be made and they are going to hurt someone. But one thing is clear, the mandates by the US government are there for the benefit of the American people by keeping them connected and keeping commerce and goods moving throughout the country for cheap and easy rates. And because there are no subsidies, you don't suffer from "sane business decisions" to cut costs simply for the sake of making more profits and cutting costs. The mandate of the USPS is broader than simply a company that makes money.