My Problem With The Sisterhood

Before I went to work yesterday, I started watching Gilmore Girls. I absolutely love that show, and I started thinking about the Sisterhood of the Traveling Pants. From the movie I then went to the books. I absolutely love those books. I think Anne Brashares is a genius for writing them, because I can connect to every character in them. But, I asked myself, why did she write a fourth book? I mean yes it tied up loose ends about Kostos and, B does truly commit herself to Eric, and the end does tie up the series. But, beside those three points why did she not have everything stay the same as it did in the third book. For one I think Lena ending up with Kostos was bad. I hated what Kostos did to her, he got married for crying out loud, and then he suddenly comes back to see if she will take him back? No don't agree with that. I felt the Lena/Paul story line should have taken off. I loved Paul. He is a great wonderful guy, and I felt that not developing him more was a mistake for Brashares. Also I feel that Win was perfect for Carmen, absolutely wonderful, and I feel that tin the fourth book she's just no where, and I definitely feel that true Carmen would always know where she is. Tibby, I truly liked where she ended up in the third book. I really really did, and I felt in the fourth she was just taking steps backwards to where she was pre-baily, and pre-brian. And Lastly B. The third book was amazing because it left off with someone who was taking care of her, and don't get me wrong I am so so so glad that Eric and her (spoiler!) end up together, but the fourth book just kind of twisted her story more than I would have liked. (I'm all about the concrete endings)