USPS risks becoming irrelevant if they don't actually start to care.
In South Africa we have the South African Post Office which has consistently and increasingly been made redundant/irrelevant by the actions of one particular organization far more so than any other: The South African Post Office
One of their biggest self-inflicted loss of relevance was due to a large strike by their workers in the early 2010's. Because of the prolonged strike people were not receiving their statements in a timely manner. At the time the law required that financial institutions send statements by post, due to this incident the government allowed the law to be changed and they were now allowed to send them by email instead.
For decades now the Post Office has had a reputation of stealing from mail. When my grandmother was still alive she used to always send a birthday card with a cheque by post to all her grandchildren for their birthdays, for around the last 10 years she was still alive the envelope I received had always been slit open and clearly "inspected", fortunately it seems they didn't feel these low value cheques were worth the effort.
Something else which used to keep the Post Office slightly relevant is that it was about the only place you could go to get your annual car license renewed. Every time you'd go there would be a huge queue waiting for the single teller who could process these while there were like 4 other tellers sitting at the other counters doing nothing. A few years back the organization which manages the licenses (not the post office) made a very surprisingly completely painless online system where you could pay by credit card and have it arrive at your door within a couple of days by courier.
In 2013 when I moved into a new house, I went to the local post office to arrange a P.O. box. To which they said "Sorry, we have none available, we can put you onto a waiting list for if one becomes available", it seems it never occurred to that branch's post master to perhaps look into making additional P.O. boxes available.
I have other stories of their general incompetence, but you get the idea. They've only been able to get away with it due to it being a government owned organization with seemingly zero effort by the government to hold management accountable for the grossly poor management, something that's pretty much the norm with most of our government and government run organizations.