(fact) America is a single market with a single language with basically a single set of regulations. Expansion is cheap in America. It makes a hell of a lot more sense to expand to another US city than it does to expand to Norway or New Zealand; but for a company in those countries, expansion is very expensive, expanding requires new laws, regulations, business entities, and languages, and shipping costs more.
(fact) America is geographically isolated from war, can't be invaded, isn't saddled with war or reconstruction debts.
(fact) Also by virtue of geography, America can produce everything: it has plenty of space to create anything it needs, from mines to farms to factories.
(fact) Americans are ambitious to a fault. I am an American living overseas, and possibly one of the most offensive things anyone has said to me here is "you should lower your expectations". I am constitutionally incapable of lowering my expectations. I don't give a shit if I live in a tiny town in the middle of nowhere, I will export millions of dollars in products that I produced here, or I will die trying; 9 to 5 in the suburbs is not an endgame for me.
(opinion, maybe fact) The consequences of failure in America are lower; in some other countries, you're forbidden from starting a new company and they will revoke your passport for some time. People don't try because there's no "try again". They also have no access to capital, essentially.
(opinion) America also siphons wealth from every other nation; for example, it seems like people are more likely to invest in public markets in America than in their own countries a lot of the time. That means access to capital on the stock market is more accessible for American companies than others. It also seems like as soon as someone gets rich overseas, they move to America.
On the other hand, it's not all doom and gloom overseas, here in NZ all I have to do to start a business is walk outside and start selling shit. To file taxes for that all I have to do is fill in my Net Income on a 1 page web form and click Submit. There's no medical debt, car insurance costs $100 a year, and nothing has a barrier to entry; I can talk to the person in charge at just about any company or organization in NZ.