As somebody who does not live and work in the US, it seems plausible to me that the H1B system helps prevent other countries from obtaining similar talent hubs as Sillicon Valley. A lot of the talent is in the US, which attracts more companies, which attracts more talent, which means it's easier to go to the US and work there and start companies there than to do it anywhere else.
There’s also the easier financing, but yes - I’m sure the outcome is dominated by the network effect of having denser talent. That’s one of the reasons Silicon Valley is so hard to replicate elsewhere.
