Largest Islands A-Z

Because Australia is considered a continent, not an island. All landmasses are surrounded by water. If all landmasses are considered islands, then Antarctica is a bigger island than Australia, and the Americas are a bigger island than Antarctica, and Afro-Eurasia is a bigger island than America.

I agree that it's hard to define what is a continent and what is an island. We demoted Pluto based on a new definition that requires a planet to be the dominant body in its orbit, which it demonstrates by capturing or removing all other bodies within that orbit. If you believe that Oceania is a continent, then Australia is clearly the "mainland" of that continent. If you consider Oceania to be part of Asia, then Australia is indeed a mother-big island, 3.5 times larger than the world's second largest island (Greenland), and 9.2 times larger than the third largest (New Guinea). I think the consensus is that it's just too big to be an island, and it's the mainland of the continent of Oceania.