This is the more interesting question, I think. 30+ years later still having dreams about exams for classes I forgot to drop, exams I didn’t study for, etc etc.
Having dreams about upcoming exams seems obvious compared to why a lot of us have dreams years and decades after your college years are over.
I suspect that it's that our brains have associated 'deadline stress' with that time period of our lives, and so to release any such stress it plays it out in dream form.
Oddly enough, I don't get college exam dreams, just (secondary) school exam dreams, and tbh I wasn't that stressed out by my exams at college, so it makes sense.
Having dreams about upcoming exams seems obvious compared to why a lot of us have dreams years and decades after your college years are over.