It is historical. We have a reasonably stable political system as does the UK and so our government has evolved through consensus since the restoration of the British monarchy.

Australia slowly but steadily made all the necessary legal changes to become a fully independent sovereign nation but we retained an Australian monarch who follows the same rules of succession as the British monarch. I expect the people who worked to obtain our sovereign independence thought the monarchy would be dealt with next. There was an attempt and it got sunk by a nasty scaremongering campaign. Some of the misinformation still circulates today and it has become part of many people's beliefs.

We need a massive campaign to educate the population so we can achieve the sort of constructive and sensible consensus that are the hallmark of our successful and stable democracy. Unfortunately both social and mainstream media will promote increasingly partisan and divisive misinformation for their own purposes. I am sure many advocates for reform don't want to deal with the hyper-partisan negativity and army of cookers that will arise flying monarchist flags. Perhaps if the monarchy is left alone they will disappear up their own arses and make it easier.