Students can (and many do) report rape accusations to the police. But it's two separate processes - a criminal process (handled through the police), and a student conduct process (handled through the university). Universities need a way to determine whether or not the accused should be punished for violating the student code of conduct (just like they would, say, for plagiarism violations or academic cheating). Even if a crime wasn't committed, it still might be a violation of the student code of conduct. It is the university's right to sanction students who violate the code of conduct and they need some way to make a determination as to whether or not a sanction is warranted.
The police, on the other hand, are focused only on whether or not a crime was committed.
In some instances, victims don't want to go to police and prefer it be handled only through the student conduct process. In these instances the university cannot compel the student to go to the police due to FERPA rules. In other instances there is insufficient evidence for a criminal trial but there may be sufficient evidence for a student code of conduct violation.
It is complex and I can see why it looks bad. But there are very legitimate reasons why universities get involved in a separate but parallel process.