Why does authors create evil characters and then make them good later on. I mean if ur cre...

Why does authors create evil characters and then make them good later on. I mean if ur creating an evil character let them be evil till the end. Not every story has to have a happy ending .And if the father killed her daughter without even giving a second thought what makes it different this time .From the looks of it even if he changes he's someone capable of killing her any moment .People don't change that easily . Like a stain on a white cloth, no matter how many times u wash it the stain will still remain