How did the Utopians manage to keep their island location a secret from the outside world for so long?

The Utopians managed to keep their island location a secret for so long primarily because it was situated in a remote and little-known part of the South Sea, far from the tracks of trading vessels and mail steamers. The island was not marked on charts, making its discovery by outsiders highly improbable. ^[1][1]

The island was discovered twenty years prior by Ambrose Miller, a member of the Brotherhood of the Better Life, who was a former South Sea whaler captain. ^[1] They also carefully hid their advanced air-ship from sight, ensuring that those in the secret had confidence in its secure hiding place. ^[1]