Why?

Because that's just the way that most girls are. They will pursue the dbag even if he is treating her like crap because the only thing that matters to her is that he has that slick dbaggy haircut, decent jawline, toned muscles and is white. Girls want guys to treat them like crap and are attracted to these types of guys and therefore this type of behaviour from the boy is having a psychological impact on her so she wants more of the thrill and she enjoys it. She likes being played around just like most girls do. It's a common issue amongst many teen girls. They pursue the dbag because they like it, even though they're just wasting their time.

If he acts nice she will stop liking him?