[adventured]

This is the correct answer, and that has cultural and economic system roots that date to the very origin of the United States.

The rest of the answer is that the US possesses an integrated, massive, comprehensive economic system. From capital markets, to VC markets, to every major industry, to the top universities on the planet, to a massive existing infrastructure related to science, engineering, programming, internet services, a total ecosystem from top to bottom. No other country on earth can match the total sum, and Europe as a whole is not integrated well at all.