You’re absolutely right that prestige has nothing to do with it (I only mentioned it to highlight an alternative that may seem to be attractive to some). However, the area of one’s study does have something to do with it. Why would he give it up the opportunity? Because he can’t accommodate all of his planned course of study (not just his college’s and his major’s general curricula). If he went aboard to study for any period of time, he wouldn’t be able to make up that time at his college in his lifetime. On the other hand, he would likely have the opportunity to live abroad if he so chooses later in his life.