It's about money and everything else too. US is a really nice country to live in for high skilled individuals. An immigrant nation who speaks the international language, a fast growing economy, especially in cutting edge tech, with overall taxes lower than Europe and even the housing market crisis is not at bad as what you will encounter in many European cities. And its huge so for a lot of emigrants looking for a new home, they will tend towards the country with the huge economy so that when they get their new passport it will be worth something.
The only downside of the US was always the immigration system.
From a purely financial perspective, a country like Denmark for example, would need to pay more than the US to be as attractive, to account for the fact that it is a tiny country where the main language is not English and where the overall career prospects are more limited.
My post was arguing that the "everything else" is more attractive in the US.
Consider a post doc or junior professor who do not know if they will ever get a tenure position or if you even want to remain in academia their whole life. Their plan B is to get an job in industry. Now consider having access to the whole US job market vs. having access to one tiny EU country. Not to mention that when you bias for cutting edge industry R&D there are industries which only have a significant presence in the US.
People value not having to step over the homeless to get to work, lower crime, free healthcare, no risk of deportation for having a view on Palestine etc etc
> Consider a post doc or junior professor who do not know if they will ever get a tenure position or if you even want to remain in academia their whole life
Now assume they are not American citizens, and travel internationally and re-evaluate the whole proposition that "everything else" is better.
The point is (as a US scientist who has lived and worked in another country, although not Denmark), the issue isn't just whether they can but whether they do. In my experience, while English is often the language of science itself in formal settings, people naturally chat among themselves in their native language and if you don't know it, you will be socially isolated, even if they switch to English when talking directly to you.
In any other gathering they will obviously prefer their own language. In countries like France, Germany, Italy out is not possible to live a normal life without being at least moderately fluent in the national language.
From a purely financial perspective, a country like Denmark for example, would need to pay more than the US to be as attractive, to account for the fact that it is a tiny country where the main language is not English and where the overall career prospects are more limited.