They do it because they refuse to face reality. As long as HE'S not admitting anything happened, he's hoping YOU will forget.
He wants to do what he wants to do, and have you accept it. He's also hoping that if he's all sweet, you'll forget.
It's manipulation and he doesn't want to face any consequences for his actions.
Sorry, but that's the way I see it.
Hugs and prayers!
Amy