I’ll assume your question is genuine and benevolent and not like my social media feed full of Europe vs USA ragebait.
I believe these economies and cultures are optimized for different things. And also I’d be precise about the country as well, since UK, Norway and Italy are also optimized for different targets. More accidentally then a cunning plan around it to be honest.
Americans as a culture are more risk takers. This is normally a good thing for entrepreneurship. They are also rather tax friendly. Which is great for capital intensive businesses like the unicorns you are asking why we see less of this in Europe. Take Norway, come here with a ton of cash and make a anthropic competitor, and you are probably a fool. Taxes alone will punish such huge capital. Less so in UK though.
But what you hear less about is the huge amount of medium companies around Europe. They have their small niche in pharma, manufacturing etc. They are often highly trusted. Often highly profitable. Often keep their people longer with lower tendencies of burnout.
But would often be seen as a failure by US vcs, as they perhaps lack a giant market to grow further into. This can lead to a lower stock price then price per earning would suggest.
Nor to say that those companies don’t exist in the US. I’m just saying the entire economy is not just lifted by companies like alibaba and google.
I’m also curious sometimes how Americans kept their risk appetite so high through nearly a century. Japan went a similar lane until the 90s crash, where after they became a lot more risk averse.
Part of my speculation here is that the US could borrow their way out of the crisis in their own currencies.