Uh huh. If they could put the package in your mailbox, they wouldn’t have to slap the “Missed you” sticker on your door, right?
I’m talking about packages too big to fit in the mailbox anyway. The last apartment I lived in had tiny mailboxes and none of those larger package dropboxes (my current apartment has these and it’s the first time I’ve seen them in my life). Any time I got a package from the USPS they just left it by the door (if it didn’t require a signature, of course).
The post office farms out it’s air freight delivery and probably a significant amount of ground delivery. It would be impossible for them to compete against UPS and FedEx without moving the freight themselves.