I completely agree with you. Too bad some of the more convenient Amazon lockers shut down. I might have to get a PO box. I'd much rather use something like Luna.
Congress passed a law in 2001 requiring any commercial entity to receive mail for another to submit a Form 1583A registering with their local post office as Commercial Mail Receiving Agency (CMRA). And then all their customers are required to complete a regular Form 1583 which is designed "verify" their identity and prevent mail fraud.
If they go without the CMRA the USPS can't legally deliver anything to them for their customers so all the small stuff you buy off of Amazon, eBay, etc are all right out. And for a lot of that stuff you're not going to know ahead of time if someone is going to send it via USPS or UPS or FedEx because it'll go whichever way is cheapest.
If they do the CMRA route then getting new customers is a big pain in the ass. I know this because I used to work for a well known CMRA and it was the Achilles heel of the business.
Perhaps it works because you can't send it to them by USPS so they'll never be the cheapest route.
Presumably when Amazon, say, are sending out an item they arrange the collection using some form of API and choose the optimal (by price I expect) delivery route. USPS would simply not be listed and so Amazon would route to Luna as expected.
Maybe it doesn't work like that, just a suggestion.
Everyone's software doesn't check names in any way whatsoever. I could send a package to: President Abe Lincoln 1600 Pennsylvania Ave NW Washington DC 20500
FedEx, UPS, USPS, DHL, everyone's software would eat that right up and spit out a label. That's because the name portion of the address usually doesn't mean anything. The White House is where it is irrespective of the person receiving the mail there.
Furthermore nearly all of the time this isn't an issue. The vast majority of all mail and packages go to the right address. People tend not to have items shipped to anyone but themselves or perhaps relatives. That's the reason there's a law that writes an exception to normal mail delivery only in the case where someone's doing it as a business (a CMRA).
And the only reason there's an exception there is that some (not all) CMRA owners 10-15 years ago didn't seem to care about preventing fraud and enough people got scammed to where it was a problem. It's expensive to scrutinize the incoming mail enough and that meant that the people who didn't scrutinize had higher profits so there was no corrective feedback through profits and losses. The only way to fix that was to make it a legal issue instead of an economic one.
The reason is that the software that FedEx, UPS, etc use to plan routes doesn't have something which maps P.O. box numbers to the street address of the post office that they are contained in. And from what I can tell the USPS doesn't publish that database, so even if FedEx, etc really really wanted to, they couldn't without spending several million (or more) to map them all manually.
It's unfortunate that it's not terribly convenient, but once you know the street address of the post office that your P.O box is located at, it's not a problem at all.