I think the reasons people move to cities in the US might not be the same as in the EU. Arguably quality of life peaks, in the US, in the surrounding suburbs of major cities. The closer you get to downtown the more expensive and the more difficult it is to do things.

In Europe I get the impression moving to larger cities actually does improve a lot of aspects of life on an individual basis.

For example, we have considered moving to New York or Chicago but what stops us is the amount of money needed and how difficult it can be just to keep up with a regular life in a city that dense and hostile.