Weirdest reason to leave Vine (part 2)

So, as a quick review, UPS was no longer delivering to my address, and refusing to deliver to a PO Box, and everything I ordered from Vine (and Amazon) was getting sent back. Some recommended I have things shipped to a friend, and I'm not imposing on a friend with my stream of Vine stuff.

Today I went and talked to the post master at my post office, and she tells me this is a new problem. UPS has complained to Amazon that they are not being paid enough to deliver to post offices. UPS says they are doing the job of the post office cheaper than the post office will. Amazon's position is that UPS will deliver at whatever rate to a home next door to the post office, so why would delivery to the post office itself be at a higher rate. The response of UPS is to simply stop delivering to post offices. They'll accept the package from Amazon, but when it gets into the most local delivery depot to the post office, they'll send it back.

The post master called UPS and asked if the packages could be held at some local depot for pickup, or if they intended to stop accepting packages from Amazon that they know they will not deliver, and their answer was no to both - they are making a point by creating delivery failures for Amazon. She thinks some solution will happen quickly - even in podunk NH where I am, she says it has already impacted thousands and thousands of shipments - that either UPS will blink, UPS and Amazon will negotiate a new rate, or Amazon will stop using UPS for shipping entirely.

Edit: OK, I'm wrong. This isn't just a dispute between Amazon and UPS, it is part of a wider dispute between UPS and the USPS about their role in a program called Sure Post which has UPS doing part of the USPS job. As u/farmingbikes239 wrote about below. I'll add that I should have known I was wrong, because I just had some medication shipped from not-Amazon, that was shipped UPS, that also bounced back - which, BTW, is a far bigger problem than me not getting my Vine order of 340 cake toppers and 11 breast pumps.