And you have missed all the subtlety of the problem. For one thing, there's no way anyone's fitting an iPad package into a mailbox, or even through a mailslot.
There's no way to distribute or update keys rapidly enough to make them general use for delivery companies and the post.
Which is the entire point: the century of mail was for mail with packages considered the exception. Special case enough to warrant needing to be physically present to receive them, or simply gambling nobody steals them when left on the front porch.
Basically you might want to take your last line there and apply it to yourself.