Then let them carry on. Most of these companies are global in nature already. My naive view of the plea for more foreign tech workers to enter the US is that the majority of those controlling the money just really really really like like in SF and don't want to leave. When there's talk of tech worker shortage, there's not even any really serious effort to look around the US. Nope, the hive mind is in SF, and they'll move heaven and earth before they have to move someplace else.