A small level of friction can reduce a lot of issues though. Without being able to tell that a package has been delivered they have to break into or open random boxes and hope there's a package inside increasing the chances they're caught and wasting their time. It's the same kind of thing proof of work anti spam measures can work under, it adds a tiny friction to legitimate users but illegitimate users have to do tons of work to send their spam or in this case open a lot of boxes.