Are all nine state, territory and federal governments, from both ends of the political spectrum, that far off the mark in their assessment of what's required?
There was also consensus about Iraq's WMD - war! There was also consensus about what to do about climate change - nothing, or only token actions. Consensus doesn't mean they're right. Note that all nine leaders agreed to exclude the various leaders of oppositions in their states, and most of them also suspended parliament. Why? Was it because they just couldn't handle another bunch of people agreeing with them? Or was it because they wanted to exclude dissenting voices? Groupthink is a powerful, powerful thing.
But let's suppose they all agree with each-other. In
Mistakes Were Made: But Not By Me they talk about cognitive dissonance, how when a person is confronted with evidence refuting an idea they have, they... reject the evidence. They can do this with the best of intentions, and the best intentions in fact make it
more likely the person will continue to believe a falsehood. This fellow encountered this:
https://en.wikipedia.org/wiki/Ignaz_Semmelweis. Obstetrics wards had three times the maternal and infant mortality rate of midwives' wards - because the midwives washed their hands. Meanwhile the obstetricians went straight from doing an autopsy on one deceased mother to delivering another mother's baby, or even performing a c-section on her. Semmelweis introduced handwashing with disinfectant on his ward, and the mortality rate dropped. His colleagues had him fired, declared insane and committed to a mental asylum.
The cognitive dissonance suffered by his colleagues was between two incompatible ideas, which were "I am a competent physician doing the best for my patients" and "my behaviour has killed my patients." Between self-image and the welfare of their patients, they chose self-image.
There's also the sunk cost fallacy, which is that because I have put so much time, effort and money into some task, I have to keep putting time, effort and money into it, even though it's obviously failing, because otherwise the first lot will be wasted. This explains everything from US defence programmes to gamblers at the casino.
Our leaders have a self-image of being people doing things for the public good. This applies whether they are old Drumpf "we'll open by Easter!" or Dalek Dan Andrews "you will obey!" They get some idea about how to do that, and then they pursue it - even if it's obviously failing.
In the case of the US, the ideas are an obvious failure, because they've preserved neither lives nor the economy, fucking both royally. Well, that's America. LOL. In the case of Australia, the health side of it has worked - apparently. That is, it's reduced infections and deaths. Great! The problem is that it has other costs in life and welfare: depression and suicide, a rise in domestic violence, older people dying essentially of loneliness, and so on. However, virus deaths are tallied carefully and reported on frequently. But suicides are tallied sloppily - we'll find out in 2021 the toll for 2020, can you imagine not hearing the virus toll for the year until 2021? and suicide deaths are not reported on (responsibly so, because news reports of suicides lead to a spike in suicides).
So the virus cost is very visible, and the other costs are not. They will become more visible in time. At some point someone may present a report showing that this level of restrictions would have been better, rather than that, and that the balance sheet of lives and misery is not as much in favour of these leaders as they would like. I've no doubt they'll react in the same way Dubya and Blair did about WMD.
The US with its overall non-response to the virus is doing the wrong thing. Australia with its heavy-handed restrictive response is doing the wrong thing. As usual, there's a sensible middle ground. But that's not as much fun as declaring states of emergency and having daily press conferences where you look serious and grim (Andrews) or clown it up (Drumpf).