You can thank, in part, a bogus NSF study in the late 80's that said the United States would not have enough STEM students, so we needed to import and give money to foreign students to fill the manufactured "gap."
Imagine having all those non-citizens in place when a country wants to retaliate. How much US business is now in the hands of foreign employees, either here or abroad? Not talking top tier, although that too. The ranks below are stuffed with non-US citizens.