Why are women afraid to report 90% of harassment’s, but not afraid to do false accusation?

I don’t understand why this is the case.

They are afraid and ashamed to report real sexual crimes (90% of them), but they are not afraid to go and falsely accuse someone of sexual crime that didn’t happen?

It makes no sense to me, they are afraid that they won’t be believed in the case of real crime, but then they are not afraid that they won’t be believed when they make false accusation? That’s totally twisted logic.