"The simple answer for that is because justice doesn't operate on the principle of what's best for the victim; it operates on the principle of what's best for the community. (That's why prosecutors represent "the people.") Particularly in a case of sexual assault of a minor, there is additional pressure to prosecute, even if the victim(s) don't support the prosecution, because interviews of convicted/admitted child rapists in prisons suggest that the rapist who only rapes once and never again has about as much supporting evidence for his existence as does the unicorn. (To wit: Roman Polanski's ensuing relationship with then-15-year-old Nastassja Kinski.) Some of those who understand this principle nonetheless argue that Polanski is now an "old man," as if old men don't rape. Unfortunately, they can and they do." – yeah, whe she said.