A system that ships millions of parcels in an almost completely automated way that has only occasional narcotics canines attempting to sniff literal mountains of packages to find one that has an ounce or less of substance that has been vacuum-sealed multiple times.

Then, they have to setup a trap in which the recipient knowingly takes delivery (and there can be no other way than the recipient signing for it, or else it would be entrapment or just mis-shipment, which is just as common) and catch them. All for a person who bought a small packet of drugs.

I think the Feds even consider such a thing a lost cause.