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.