Answered by The Community. Making the world better, one answer at a time. The reason for it being a world heritage site is because it holds so many beautiful features like fish, coral and mammals. The Great Barrier Reef is UNESCO World Heritage listed because it is the largest coral reef in the world.By having World Heritage designation, the Great Barrier Reef is acknowledged to be of value to all people and is to be preserved.nswered by The Community. Making the world better, one answer at a time. The reason for it being a world heritage site is because it holds so many beautiful features like fish, coral and mammals. The Great Barrier Reef is UNESCO World Heritage listed because it is the largest coral reef in the world.