Check the details on that ngram, it doesn't capture "disappeared" as a transitive verb. Virtually all the examples are variations on "Once the item had disappeared, it was never seen again."

“Disappeared” in the sense used here refers to domestic opponents being covertly kidnapped—and usually murdered—by their governments; a usage that originated in connection with Argentina's “Dirty War”, but which has been used for many other situations since.

The use of “disappeared” this way here I would say I is very conscious commentary in itself.

It's used in the same sense that people would say that the KGB 'disappeared' people.