Murali Tumahai:
It’s a combination of less variety in Australia compared to the variety found domestically for us Americans, along with dipping into our very nearby neighbors (I’m American, and have lived in Australia for over a decade - I have a fair grasp of what can be found in each location), and island fever.
Admittedly, it’s a very, very large island, but island fever nonetheless. I live on an island chain (Hawaii), and while we are literally in Paradise, that sense of being trapped is pretty real. You just start thinking and thinking of ANYWHERE to go to get off of the island.
As for variety - yes, Australia has Alice Springs, and the Whitsundays, down through Sydney, into the interior Outback, and on through Melbourne - but you have nothing like going from Alaska, through Kansas, and Portland, swinging by French New Orleans, dropping by Cuban Florida, New York, Sante Fe, LA, and ending up in Hawaii. We don’t even have the same local languages in some of these places. Australia has variety, but nothing like the US.
So when we are looking at our limited time schedules, and looking at ticket prices; and then trying to get the most bang out of it, we very frequently just do a road trip, or a 3 hour $150 ticket, to a closer location - and in the US, that still means domestic, usually.