Obviously quite a lot of it is remote desert, so obviously not that conducive to large-scale habitation.
However, much of Australia has a reasonably favorable climate. Yet there are relatively few major cities outside of the big dogs -- there's Geelong, Wollongong, Gold Coast, and Central Coast, which all seem kind of secondary cities or overspill from the bigger nearby cities, and then that just leaves you with Newcastle, Townsville, and Cairns, none of which are that big. Why are the rural areas on the wet east coast still so lightly populated and remote?
Australia and New Zealand both have extremely poor soil that make us unsuited to intensive agriculture pre mechanisation and fertiliser. Rather than settling hordes of small family farmers like the Jeffersonian ideal of agrarian America our rural lands were filled to the brim with sheep and cattle, whose farming requires very little permanent labour. Traditionally sheep are only shorn or slaughtered once a year.
The one area with somewhat more concentrated rural settlement is coastal Queensland, as it was prime country for sugar cane whose production is significantly more labour intensive.
Even today with modern agriculture Australia and New Zealand's farming lands are comparatively unproductive, and require less manpower than agricultural efforts in more fertile regions like the midwest or ukraine due to the lower yields.
