It’s why she tried desperately to clean up after him. Daisy needs to believe she married the right man. She needs to believe he is good. And that he will be a wonderful father. And that he loves her. Because what is the alternative? Daisy refuses to accept the alternative.
Why should we always “understand” our abuser, the villains, the mendacity of evil, the people who let us down? Does understanding help us heal? I don’t think anything really heals trauma. You just find some kind of narrative to learn to cohabit with it.