The "bigness" of an area, doesn't relate directly to its carrying capacity long term population.
Desert areas have a very low carrying capacity, as do mountain tops, and other inhospitable areas (i.e. with bad soils, bad water, etc.).
Australia is not alone in far exceeding its total long term carrying capacity by allowing gross immigration.

Before every action and decision think of the consequences 7 generations into the future....Ute Rule of Life