The issue is that sexual assault is notoriously difficult to prove, so the vast majority of cases don't lead anywhere. It's typically not worth even reporting it because unless you have a hidden camera or there were witnesses watching who are willing to testify, there's not much you can do. So, in an effort to protect victims, universities tend to have their own rules that are more enforceable. The standard is lower (preponderance of evidence instead of beyond reasonable doubt), but the punishment is also much lighter (suspension/expulsion vs jail time and sex offender status). From what I understand, students usually don't get much of a punishment if there aren't other alleged victims. It's usually not just the one instance, but the university determining that the alleged perpetrator has a pattern of assault or harassment.