Simple. If an alleged rape is turned over to the police, then criminal prosecution standards will apply. Evidence is gathered, testimony is obtained and - most importantly - a presumption of innocence applies.
This leads to what the proponents of these alternative proceedings believe is an insufficient number of convictions. Accusers could have to continue to see the people they have accused on campus, with no sanctions taken against them. And legal proceedings do not comply with the Title IX directives handed down from the Obama Administration, which says that the standard should be “a preponderance of evidence” - 50% + - rather than “beyond reasonable doubt” in such cases. So to apply this lower standard and to raise the number of convictions and penalties against the accused, these alternative proceedings are being used.
Fortunately, there are more and more accused who, once having been sanctioned by such proceedings, are using Title IX itself to sue the schools - and win. It seems that Title IX says that you cannot discriminate on the basis of sex. It had not occurred to anyone that such language means that you cannot discriminate against men anymore than you can discriminate against women. That seems an unnatural concept to them - but the courts say differently.
Feminists believe all sex is rape therefore all sex should be convicted as a crime. By feminist rules that means a 100% conviction rate so the rules are meaningless.