“For more than 100 years beginning in 1776, the island was used as a quarantine station for those suffering the plague and other diseases, and later as a mental hospital. Because of this, the island is frequently featured on paranormal shows. The mental hospital closed in 1968, and the island has been vacant since.” (wikipedia).
It is possible that the Island was selected as a quarantine site due to its situation in relationship to wind currents. They blow any possible hazard from the island away from the city.
Contributed by: Craig Martin