It may be that each collegiate cross country program in the United States is markedly different from all others, just as it is predictable that many high school programs also vary widely in scope and intensity, so listing absolute generalizations of the differences between high school and college cross country is a difficult task. Many high school programs are relatively intense in training and personal development, a pair of characteristics that many colleges echo. However, it is possible to give several distinct areas where you may see drastic changes.
College programs expect a certain degree of initiative and self-starting.
Many levels award financial aid and part of that package is a tacit or explicit understanding you will give your best to the program. That may require completion of workouts when the coach is not around, monitoring of diet, weight, rest, or academics with very few coaching intrusions and establishing priorities of running and academics without constant harassment from a coaching staff. You are expected at a college level to be professional, mature and forward-thinking. At a college level, much more communication will be initiated by the athlete. The days of a coach constantly checking how you feel expire after high school.