College grades are generally 60% midterm & Final, and 40% everything else (smaller papers, participation, other tests). From what I’ve seen, Freshman that flunk a course (or do poorly) get behind early on, new found freedom and no helicopter parenting to remind them to go to class and do homework. Its hard to come back from an F on the mid-term. Everything is riding on the final, and they may be too far behind to do well enough to counteract the bad midterm.
Time management is probably the biggest culprit. Parents are so overbearing in high school - managing all activities and study time/bed time that the new found freedom produces poor results.