If your talking about making into a movie, It's so people could see it how stephanie saw it. Her view became your view. 阅读 the book 你 could imagine many things for Bella but in the movie 你 see the only face for Bella, Edward, Emmett, etc. Also because the 图书 were a hit then why wouldn't the 电影院 be a hit? People would make a lot of money and those playing the main characters would be known world wide. If your talking about the book it's a simple answer. See Stephanie had a dream which made her sit down and right it. She got engrossed with it and ended up making a whole saga. I mean it can happen. Plus 写作 is a passion to her. Maybe she just wanted to make a new era a 吸血鬼 to.
