Because a university isn't investigating to determine whether a crime, per se, has occurred, but to determine whether allegations of discriminatory (racial, sex

Because a university isn't investigating to determine whether a crime, per se, has occurred, but to determine whether allegations of discriminatory (racial, sexual, etc) harassment are credible. If such harassment is occurring, or something equivalent which creates a discriminatory hostile environment for the student, a university has an obligation under these laws to end it. A rape is a crime, but a rape followed by the ongoing presence of the rapist also equates (under legal precedent) to a hostile environment for the student victim, which is how Title IX comes into play. The question was why are universities conducting these investigations. Rape plus ongoing presence of the rapist is considered a form of sexual discrimination by the university, in so far as the university willfully permits the rapist's ongoing presence. Thus the university is put into the position of judging the credibility of any allegations. In this way it's also identical to the racial epithet scenario. Shouting racial epithets isn't a crime or even illegal, but a university that doesn't stop such ongoing behavior among its students is considered to be illegally racially discriminatory against the target of the epithets.