Because as Draco so eloquently put it, insanity is doing the same thing over and over again and expecting something different. And that is exactly what she was doing. Knocking on the same door and expecting someone new to open it. Draco was, well,  Draco. Sometimes he answered the door as a sullen, broken shadow. Sometimes he was a changed person, one that felt grief, love, empathy. Other times, the man who answered the door was bitter, defensively hostile and downright abusive. He would push until she left, pull her in so tightly it hurt, then push her right back out. 