Moreover, it was meant to emphasize that government can (and does) make, and force its subjects to abide by the silliest of rules - because, just because.
Of course, whenever you set a limit, there's the guy whose box is two steps beyond.
I have one of those oversize mailboxes so I don't have to take the stupid card 40 miles round trip to get most packages, only to find I've arrived at the post office when the postmistress takes her break .