From my personal point of view, and based on my personal history as a victim of Australia's heinously racist White Stolen Generation (and who was eventually returned to my birth mother because of her strong will), Australia is a totalitarian-authoritarian fascist hell hole that got away with genocide, and will bend over backwards to function as a lackey for the US' military-industrial complex. There's not a single racist war that Australians won't follow the USA into fighting. See also: Pine Gap.
My personal reason for leaving Australia is that I don't want to participate in a racist society. Read its constitution, its an utter embarrassment.
Tourists don't often get through this bubble, seeing only the shiny bits, but for those WSG's of us who grew up in the countryside, also with Aboriginal friends and family members, the dark underbelly of Australian society rubs us a bit raw - or at least it does in my case. Casual racism in Australia is like none other in the world, and I find it detestable, personally, so I have no desire to participate in its economy. I left as soon as I could, to follow my own American dream - which reality quickly revealed was little more than a Disney fantasy.
Europe has its own problems - sure, the Ukraine war is a catastrophe of uniquely European origins - but I'd much rather live in a country that isn't involving itself in the worlds wars at the moment. Austria has been an absolutely great place to raise kids with a cosmopolitan, international attitude that will stand the test of time - of course, there are always exceptions to the rule, but in my personal case, its just been a better place to live, period. Only issue I have is the weather can be hard for someone who grew up on the beaches and in the outback, but the spring and summer always makes up for it.
The thing that truly disturbed me about life in the US was its nationalist groupthink, which seeks to justify the atrocities the American people enact on those cultures its ruling classes have deemed inferior. Same is the case with Australia. I guess I freely admit, that as a foreign ex-pat living in a non-native bubble, its a lot easier to avoid the groupthink by just moving to Europe - where of course it also exists in spades - but I'd rather live the life of a refugee or interlocutor than participate in the Wests' heinously racist wars.
My kids have been raised multi-lingual, speak German/English very fluently, and are also learning Russian and Ukrainian in school to prepare themselves for a future where Austria is, once again, a safe place for citizens of both countries to co-mingle, as they once did. That is a forward-focused quality of life issue that simply doesn't exist in either the USA or Australia: the kids in this part of the world actually want to learn each others languages. Just like it was the norm in Aboriginal cultures, incidentally. (You were considered defective if you only spoke one language...)