[mafribe]

I know what it is like to cheat and not to cheat: I cheated like crazy in high-school in my weak subjects, but didn't cheat at all at university because I was the best student in the year so copying from others would have reduced my grades.

    Why would anyone not cheat? 

You forgot the most important reason: to learn. In some sense cheating is a self-punishing crime, because the cheaters forgo the learning opportunities that courseworks and exams offer. Indeed the only reason universities have to have graded courseworks and exams is to put an incentive structure in place that focusses student attention. In a way grades are an anti-procrastination framework.