First let me say I think time management and being on their own for the first time plays the biggest role in whether a student goes off the rails in college. Another aspect which has been touched on some in this thread is test taking ability. In HS there are plenty of chances to get easy points like homework and another assignments. There are less of those in college. You end up relying on more on your general ability to take tests and show you know material.
I think some kids just don’t test well. I know there is evidence that ACT/SAT results don’t predict success in college perfectly. But being able to take tests well has to be a factor in doing well in college.