I don't know whether this has anything to do with the contractor vs employee nature of these companies, but I do know that UPS is way better at actually doing their job.
He even collected the strewn around mail from our mailbox the other day and visited us to let us know that someone has likely been stealing our mail and that we should check our credit cards. I'll miss him when he retires soon.
Other time (more an issue for Amazon in that instance) they delivered item but never scanned it so an opportunist could claim that item was never delivered and there's no way to verify that.
As I said there are also good things. I really like that USPS doesn't artificially delay packages like UPS (if item could be delivered sooner, but was paid for 2 days delivery, they will hold it). I for example had a package delivered next day because it was shipped from a close place, even though the estimate was 3-5 days.
This happened to me during tax season no less. My only saving factor was that they put it into the mailbox of a relative who lived next door (and their last name is significantly different from mine) imagine a total stranger with my tax refund plus all that information. Thank you incompetent USPS employee. We definitely complained about them, not sure if they've sorted that out but I also bought a book not short after that, and you guessed it, my relative got my book instead.
The other delivery companies just drop my stuff off there or, if they aren't open, they'll drop it at the gas station/convenience store. UPS has gotten stuck on my lawn, twice. FedEx can never find the house. So, it is just easier this way and the post office has been very accommodating.
It is one of the great joys of living in a very rural area.
It took ten days (counting from the 1st delivery attempt), and as far as I can tell five separate delivery exceptions (with the same address that I've used for any other delivery service, including FedEx 2nd day air), for them to finally deliver it. And guess what happened when I finally opened the package? The phone that is supposed to be in the package is gone (this is a pixel XL phone ordered from Google Store; fortunately Google is very responsible with this and in fact when I explained the situation to them they immediately acknowledged it to be a problem they are aware of)