Since graduate students do work for universities at low wages, it seems like the universities are getting a good deal.
So how do you want to account for labor costs? After they leave, the work got done and the workers got paid. Both sides benefit from this arrangement, though you can certainly argue (and many do) that the benefits should be split more fairly by paying the workers more.
Separately, the US would benefit from letting them stay and do more work. But that's generally the case for any immigration restriction. They get in the way of mutually beneficial private arrangements. US employers can't hire people who are willing to work for them, and the workers strongly benefit from being able to work in the US. Immigration restrictions are all about the government getting in people's way and the various justifications people make for continuing this interference.
So how do you want to account for labor costs? After they leave, the work got done and the workers got paid. Both sides benefit from this arrangement, though you can certainly argue (and many do) that the benefits should be split more fairly by paying the workers more.
Separately, the US would benefit from letting them stay and do more work. But that's generally the case for any immigration restriction. They get in the way of mutually beneficial private arrangements. US employers can't hire people who are willing to work for them, and the workers strongly benefit from being able to work in the US. Immigration restrictions are all about the government getting in people's way and the various justifications people make for continuing this interference.