If they're from a foreign culture or country then they've already given up on socializing with their own people by becoming exchange students. Theoretically they could learn or gain something from local kids, if kids had anything useful to teach them, and if they planned on staying after graduation. But if they don't plan on staying, then no matter how much or how little socializing they do, they'll just get one line on the resume or a checkbox at job time so over-investing in socializing won't help their future. So they may as well at least get something out of the classes, by learning as much as possible from the profs. Which they need to do, if a GPA of 2.0 and the right local friends is as useful in the job market back home, as a GPA of 4.0 from some foreign school and no local friends because they were at the foreign school.

From their point of view, maxing out their GPA is far more useful than getting drunk with people who won't matter to them in a couple short years, and being kids, have nothing to teach them anyway.