The plates and interpreters were passed from Nephite seer to seer, most of which were kings. Moroni preserved the records and interpreters and then passed them to a latter-day seer and king, Joseph Smith. It is the mysteries of God which convince people of the truth and the error of their ways.
Like the Nephite seers, Joseph Smith was supposed to personally deliver the the interpreters to a successor designated by the Lord. This never occurred. The modern Church does not have the interpreters.