This is coupled with us having the lowest population density in the world for a population over 10 million, which helps a LOT when dealing with a sickness that spreads nominally worse with proximity.

For what it's worth, this was likely not due to political cooperation - the PM and right-wing media have done nothing but try to lambast states with opposition control to try and push their own agenda on the back of the pandemic. Daniel Andrews has been dragged through the mud and back for taking the lockdown measures that he did with Victoria, despite it being broadly successful in the end.

I'm no epidemiologist but if I had to guess, a mixture of our naturally low population density, a relatively low influx of carriers and a dash of Australia's famed dumb luck are responsible for our performance in the pandemic over anything else.