I think part of that is it's very hard for them to look at themselves and admit what they did. I think when they come back they sometimes feel extremely guilty, know they've caused tremendous pain and disruption, but basically want to forget it ever happened. It's kind of like having a new pet in your home. They are not quite comfortable, don't know what's going to happen, appear ready to bolt at times, and have difficulty appreciating affection until they get used to the surroundings.
There is no arriving, ever. It is all a continual becoming.