> There are good things there of course, first and foremost the salaries and the nice suburban houses
Australia has lots of nice suburban houses too. But they are expensive, and you'll struggle to get paid enough to afford one. One advantage the US has over Australia – while it has really expensive areas like the Bay Area or Manhattan, it also has lots of medium-sized cities with affordable housing and plenty of jobs – Australia's population distribution is much more lopsided, and the parts of the country with affordable housing tend to have quite limited employment opportunities, especially in fields like IT. (Remote work can help there, but Australian corporate culture is behind the US in acceptance of remote work, although COVID is helping to change that.)
> On average North Europe is way happier than the U.S but not as many people wanna move there (can be partly explained by the language barriers but I think it's simply people thinking that more money = more happiness).
I wonder if the weather is also a factor? The US – even just counting the 48 states – offers a wide variety in climates – Michigan in winter is colder than Copenhagen, Florida's winter is quite pleasant. Not everyone likes snow.