I'm an Australian citizen who has lived in the US for fifteen years.
This law (and others) say that if I want to travel to see my elderly parents in Australia I have to:
1. be fully vaccinated (I am, have been since December) - not too unreasonable
2. quarantine upon my arrival for two weeks (inconvenient, but not unreasonable - unless they are on their deathbed, gravely ill, etc.)
and adds this:
3. am prevented from leaving Australia unless I "prove" that I have permanent residence elsewhere (which makes little sense because as an Australian citizen, whether I do or don't, I'm still entitled, subject to points 1 and 2 above, to return at any time - for the same reason that Australia won't release my superannuation (401k-ish kinda thing) regardless of my residence elsewhere, "because as a citizen, I am entitled to return at any time, so that money needs to stay until the appropriate time").)
Note that they talk about "obtaining exemptions", but there are multiple examples, including one in this article, where the government has stated "charter a plane for your trip, do not fly commercial" in order to obtain the exemption. Which makes one rule for the rich (and you have to be rich to charter a plane in general - even more so when most countries, with the exception of New Zealand, are at least an eight hour jet flight away, so this is not so much "charter a Cessna" as "charter a G450 or Global 6000" - hint, those aircraft are in the _five digit per flight hour_ charter range - Melbourne to LAX is probably a $100,000 flight, at best.