Likely because no one with a knowledge of Australian data sources has taken the time to create one - or at least not referenced it here. I see some commercial and some free ones listed in a google search. Have you checked mapcenter2 and/or googled for one?
Australia is not listed in the dropdown country list so you may not have noticed my world mapset.
The source data was at 1:1,000,000 scale which would make it more for general reference - better than the built in world map but not 'standard topo map detail'.
Australia is big. Were your interests more city/road oriented or outback areas?