Earlier quoted context omitted.
How is ensuring checked bags have boarded passengers not also theater? Airlines openly sell unattended cargo space on passenger flights and it's screened the same way as checked luggage.
Do you get to specify the plane it goes on? Can you purchase it untraceable, the way you can you a plane ticket with a prepaid card, check in and check luggage without any ID?
You also can't buy a plane ticket for an anonymous person. It has to be for a legal person, which the government is informed of before the flight takes place. That ID is attached to the luggage when it's checked, which is how they can implement bag retrieval when the passenger doesn't board. I'm sure there's an airline somewhere out there accepting checked bags without tickets or ID, but it's not supposed to be allowed.
For air cargo, someone provides an ID, but it's usually the shipper or some other person with no real involvement beyond working in the supply chain. There's a chain of check boxes that says "I received this from an entity I have a legitimate business relationship with" and that's good enough in practice.