"Licensing issues" seems to be the standard reply. But, why would licensing in Australia be different from licensing elsewhere? Isn't a show streamed to Australia is just as profitable as a show streamed to Europe or America?
Yes, but Netflix must sign and *pay for* a license in each separate territory. The company pays per show/movie, per market, per year (or whatever licensing timeframe), and it doesn't make sense to roll out an actual service until you have the rights to a decent content library in that new territory.
Netflix is working on licenses for Australia, but doesn't have a service yet. And whatever agreements it did sign so far likely don't become active until Launch Date X.
So as usual, it all boils down to costs. Follow the money.