Australia has a natural advantage -being an island continent.
With the first wave, NSW was the worst affected - from returning cruise ships when the appropriate steps weren't taken We learnt from that original error -and quickly shut down our national borders to overseas travelers. (People had to stay in mandatory quarantine for two weeks in hotels.) This was successful in NSW because appropriate people were used - the military and police.) However, in Victoria quarantine responsibility was given to private security companies -who didn't have the appropriate training. It got out of hand very quickly -and the virus spread into the community. This then spread to workers in aged care facilities who infected many elderly -who died.
Even today, most new infections are to found in overseas travelers returning home - thus, it seems logical to put those returning by air or ships (the only way) into mandatory quarantine for two weeks.
Believe me, with such comparatively low numbers, most are just relieved to be coming home -and are willing to put up with the inconvenience. That's not to day that there are always those who feel entitled that the world should revolve around their specific needs and grumble -despite realizing how fortunate they are to live in a part of the world with so low numbers of infections and deaths.
Quarantine is part of our history. When immigrants came in sailing ships they were quarantined -so as not to introduce serious illnesses. (sadly, when white settlement was first established there was no quarantine - and our aboriginals died from illnesses such as measles - a national shame!)