It&#x27;s because it&#x27;s on the periphery of the Law&#x27;s effective reach.  It&#x27;s very hard to prove, beyond a reasonable doubt, what happened between two people behind closed doors. Especially when the only evidence is the allegation itself. Rape kits have helped with this problem, but they often can only show that some sexual interaction happened, not indicate whether it was consensual or not.  It&#x27;s even harder to convict when the charges are brought years after the alleged crime, as is often the case.