My understanding is that scientific research has a dual problem, where the number of students needed to carry out existing professors' research is much larger than the number of junior faculty positions generally available. The result being that most trained PhDs must leave (US) academia because there are no jobs for them. In fact, I've heard scientists complain that universities owe it to students to provide more help finding a job in industry after they graduate.
Given all that, where are professors supposed to find and hire students who don't want to stay in academia themselves? I think a lot of these students wind up being aspiring immigrants, and I'm not surprised that a lot of them would also have a hard time finding a place for themselves after graduating and that many of them would leave. Also, the abstract seems to argue that that US still benefits greatly from this arrangement: "though the US share of global patent citations to graduates' science drops from 70% to 50% after migrating, it remains five times larger than the destination country share."
Given all that, where are professors supposed to find and hire students who don't want to stay in academia themselves? I think a lot of these students wind up being aspiring immigrants, and I'm not surprised that a lot of them would also have a hard time finding a place for themselves after graduating and that many of them would leave. Also, the abstract seems to argue that that US still benefits greatly from this arrangement: "though the US share of global patent citations to graduates' science drops from 70% to 50% after migrating, it remains five times larger than the destination country share."