At the risk of speaking out of turn, I've traveled extensively outside the US and befriended a lot of folks and had discussions on this topic with them. I would summarize my findings as such:
1. Economic Mobility: In Europe economic mobility, on average, is actually better than the US. But, for those who are educated and driven, economic mobility in the US is much much much higher. Average person may up their income by $10k/yr in PPP or more in Europe from young adulthood to adult-hood, average person in the US tends to stay flat. But driven, intelligent people with degrees in the US can double or triple their income from young adulthood to adulthood, and this simply doesn't happen in Europe. The tech industry is a major factor in this, where senior-level positions in non-FAANG companies can make upwards of $150k/yr in the US, and the PPP equivalent European salary is around half of that.
2. Lifestyle goals: In Europe, it is very hard to be successful as a young person outside of major metro areas. This is somewhat true for the US as well, and while business cultures are different in different areas, it's easier (pre-COVID) to work remotely for a US-based company vs a EU-based company, but usually requires working US timezone hours or relocating to the US. Additionally, Americans tend to lead faster paced public lives, but slower paced private lives, and the reverse tends to be the case for Europeans. Everybody has their own lifestyle preferences, and lifestyle also is a major factor in intra-EU movements as well (I have friends who moved from Belgium to Portugal for instance, due to lifestyle. Friends that moved from Germany to Spain, etc.)
3. Freedom: The US is more diverse and free in some aspects. There's a lot of nuance here, but while you obviously have a lot of history, linguistic, and food diversity in the EU, there's significant similarities in cultural expectations, especially in professional work environments once you enter the middle class. The US is a LOT more free in regards to one's behavior, lifestyle choices, and personal life when you are in the middle class, compared to Europe. This is probably more obvious in the UK than anywhere else, where class hallmarks are as direct as how you speak to someone verbally, where in the US it's possible to have a pronounced Southern accent and still be solidly middle class in a professional environment, even though that's not considered as high-brow as a West-coast accent would be. Europe is in many ways more diverse overall, but not really in the middle class and above environments. Also some people just want to be free to do whatever they want on their own property without anyone nosing in, and this is antithetical to the European communal mindset which is very often enforced legally through direct government regulation.