I read they are popular with drug distributors. They ship their merch world wide using various hidden channels and couriers and this helps keep track of the merch.
Sounds like one of those "what if..." things someone made up.
AirTags are terrible for surreptitious tracking, alerting every iOS user nearby of a tracked product following them around.
I mean, years ago people, such as stalkers, would use it for this purpose, but Apple rightly gimped that. There are a lot of specialized, self-connected trackers that creeps and criminals use.
I put one in my car when I shipped it across the country - it was great to be able to check where it was and know when it was getting close!