They are afraid of getting stuck in the system
I think another reason people don't report is that they are afraid of getting stuck in the system. So like, some cases do not necessarily go all the way through. Or, in the rare case, it will be that there is not enough evidence or that sort of thing. Even just the digging that's required is quite traumatizing, I guess. So, some people might be afraid to revisit that trauma. There is also that piece of getting stuck in the legal process- that might be why they are unlikely to report.
Emphasize the victim's right to decide whether they would like to report the incident after they have disclosed it to the university. Ensure the victim is aware of the formal and informal routes for reporting, including the option of reporting to the police. Clearly communicate any limits to confidentiality.
Provide students with information about what can serve as evidence of sexual assault for the purposes of a university investigation. This information should appear in the policy itself and in educational materials about the policy.
Within the policy and educational materials, provide information about possible timeframes for the completion of an investigation into a report of sexual assault. Deliver regular, scheduled updates on investigations to complainants and respondents. Such updates should be integrated into the policy.
Offer fictionalized but representative examples of how disclosures and reports to the university have been handled.