That's not why "most" domestic violence charges are dropped it has nothing to do with being a master manipulator. Most charges are dropped because the couple makes up or the victim no longer wishes for it to go forward. Ive known many cases where the couple split up and are no longer together and the victim just wants to move on with their lives. Court cases take months some times a year or more to come to trial. If the victim has moved on with their life they dont want to come to court and face the attacker again. OR they couple has made up and are happy again and again the victim wants no further action. OR what also happens is the victim exaggerates the claim of assault during the heat of the moment because they are mad and months later they are over it OR a suspect and victim work out a civil $$$$$ arrangement to get the criminal charges dropped
But you are correct in that just because a case was dropped has nothing to do with guilt or innocence.
They "make up" because the abuser manipulates the victim into believing that they have changed, and it'll never happen again. It does, of course. And virtually always escalates.
Most abuse victims are abused badly enough to end up in the ER multiple times before they actually do anything about the abuse. Going from memory, I believe the statistics are that they'll be treated seven times (on average) and hospitalized once.