For example, it's completely possible that salaries in London are higher than in New York or San Francisco, given the high cost of living in London.
It could also be that there are more US-based UX people working in major US cities so that the average US salary looks higher.
Or maybe the sample size wasn't high enough to control for these kinds of regional differences.
So, while this data is directionally interesting I wouldn't apply it too much to your particular situation.
I believe this is the case in tech
But, I think most professional jobs are like that. Lawyers and Doctors also make far less in Europe than in the US.
I think that overall in Europe, there is a much less steep income curve as you advance your career, skills, or education. This is good for the majority of people, but bad for your typical HN'er.
The US really has no equal if all you care about is making a shitload of money.
I don't understand; how is this good for the majority of people?
This has several benefits outside of money: more integrated and coherent society (no "white trash" next to yuppies), less homeless people, less incarcerations and violent crimes due to being poor/uneducated/without future/etc. And more people thinking as part of the whole of their country/society, as opposed to "screw others, I just need to get to the top myself".
That said, some advanced countries, like Britain and (less so) France, do resemble the US more, compared to say Denmark, Sweden, Switzerland, Netherlands, Italy, etc.