Earlier quoted context omitted.
Foreign science grads are what is driving the US as a leader in R&D. Look at the post-docs at labs in MIT, look at the US Nobel prize winners - the majority of them are immigrants If companies are limited to domestic scientists then they'll quite happily move their R&D departments to countries with more relaxed immigration laws. Foreign universities will happily take the best researchers from around the world that ar…
The elephant no one seems to talk about is: Why are universities not accepting more "local" grad students? In my experience, it was the standardized tests. I was completing an undergrad in math while attempting to the GRE. Meanwhile I heard stories of students in other countries essentially focusing on the GRE as their undergrad equivalents weren't as time consuming/rigorous.
The elephant in the room isn't why aren't more universities accepting 'local' students. No department would choose a foreigner over a local. You wanna know why? How much the student is going to cost them. Foreign students never qualify for in-state tuition (well at a state school anyways) and right off the bat are much more expensive to their advisor's budget. Local students can also apply for NSF Graduate Fellowship, and bring in their own funding, something most foreign students can't. Both of these factors make it so that the first preference is to hire local.
That said, in a large number of departments (especially in CS, and other sciences) you see a burgeoning international student population. Why? There just weren't enough decent local applicants to go around and science needs its foot-soldiers.