Could also be homesickness, grades, not clicking with the team, a perceived miscommunication of expectations... really it's hard to pinpoint just what the situation is with each kid.
Back when I was in the middle of my teaching career, I found myself with a new student. He was a transfer from Ithaca College. Now, my school was and is pretty good, but Ithaca is a better school on every measurable and the kid had done well there. I asked about that and the following dialog ensued:
Me: Why'd you decide to transfer?
Him: I hated Ithaca.
Me: But it's a nice school (it is; I had been there before), well regarded, and you were doing well there. Why didn't you like it?
Him: I liked the college. I hated Ithaca.
Me: You left a good school where you were doing well because
you hated the town it was in?
Him: Uh-huh.
Me: <Astounded look> Well, ok. Let's get you registered.
I shared this story with our recruiters and was gratified to hear later that they were referring to the "Ithaca Effect" when a student they had worked hard to recruit and retain left us for no good reason that anyone - including the kid - could come up with.
You can see this in every field of human endeavor, without exception.
