What makes a woman think that having a baby will better a relationship that's on the rocks?

Babies are cool and all but they come with a lot of responsibility and stress, and adding all of that to an already stressful situation is bound to make matters worse. I've got a friend who's been with her boyfriend for a little over a year, and for the past several months their relationship hasn't been so great. She recently found out she's almost 3 months pregnant, and her thinking is that this baby will make the relationship better. I've tried to tell her in very nice ways that she shouldn't get her hopes up, but she won't listen. She sincerely believes this baby will make things all better between her and her boyfriend, but from the way he acts... it ain't workin. I just don't understand where this thinking comes from.