It's very interesting to ponder how our proclivity of huddling together in tight cities can cause such anomalies.
For any given 'feature' in a suburb (shopping centre etc.) the houses in walking distance will have a higher value. If you have several multi-family homes or even towers you have a large supply of walking-distance-dwellings. If you have a bunch of single-family houses (the common thing in Australia) then you have low supply.
In other words, Australia tries to huddle together as least as possible which causes many weird anomalies (don't get me started on quality of life/walkable suburbs/rise of US-style drive-everywhere-life with increased obesity/etc)
Any stat comparing population size with land mass is misleading. Australia is hot, 300km off the coast and you’re in drought territory. Go in further and you won’t last a day in the sun without shade and water.
It’s not the US, there are towns in the outback, the majority choose not to live there. People will ordinarily group together in a single area where jobs, infrastructure and general quality of living are high.