[garbawarb]

Because the US is, or for a long time has been, just the best place in the world for so many things. Want to be a SWE grunt? You'll earn twice the salary in the US. Do you have startup ambitions? There's nowhere better than the US, specifically the Bay Area, in nurturing and scaling a business. Filmmaking? Hollywood is the place to be. If you want to be at the center of fashion or finance or contemporary art, NYC. US dominance might be changing but a place being the top of a field means it attracts the best of the best from around the world, and for an ambitious person, the best place to be is among them.