Several reasons.

Top talent has the world as their oyster: for the best the answer is obvious even when it is a 96% fit vs. a 96.5% fit.

I don't know the actual %, likely gap used to be much bigger, but point is you can get very sudden state changes in outcome from very small policy change when at that point: think idiom "it was the final straw that broke the camel's back".

Self sorting: the best see that people like them went to the USA already, because those forerunners saw their talent, advise them to join them in the USA.

This one depends both on political stability and everyone not leaving/being kicked out.

Money: especially for startups, especially for tech. US trade deficit and reserve currency enables this as all the dollars have to make it back to the USA somehow, and investment is a somehow.

This one also depends on political stability.

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HelloNurse 2 days ago | parent [-]

> This one also depends on political stability.

Canada is going to be seen as similar to USA, but open to immigrants and not fascist. Will it develop enough opportunities?

	▲	ben_w 2 days ago \| parent [-]
		Canada might be able to do that, but do also remember that the USA's president keeps talking about making Canada into just another state. There's a big risk that everyone says "I want to be in the country that wins the next war. Therefore, China." and this then becomes a self-fulfilling prophecy because all (or enough of) the talent made the same choice.