I agree, but how many people come here from, say, India or wherever, work in IT in somewhere like SF and say ok I've had enough training, time to go make my country a better place? None. I don't blame them either.

Actually there are a LOT of Chinese and Indian entrepreneurs I know who moved to the US, worked here, and especially back in India are now building SV-style companies there. Or are putting parts of their global businesses there -- given how expensive labor is in the US and especially SV, it's a huge competitive advantage to be from, say, Ukraine and be able to set up a great engineering organization there.

I agree it makes less sense for an individual worker to move back (unless there are family or other concerns).

It depends on person, as usual. For many, the US residency is a blessing. Things are nice here, compared to where they come from. The quality of life is much nicer, and this is something i'd most definitely want for my kids.

However, there is also a greater advantage to going back home: Those markets usually lack the capital and the knowledge, and it's relatively easy to copy startups from here and implement them in their home countries.

That is most certainly not the case. While there are many who stay, there are also a sizeable number who go back to their home countries.