Yeah, I see your point, but if you think of it, all the info we have ever gotten about Mother Theresa has been about how unwaveringly devoted she is. Years and years and years of hearing that. So, we already know that side of her. These writings pointing out the doubts and anguish she had offer a small glimpse into another side of her. She was, after all, a human being. By saying this is all a ploy, you are negating a part of her. She is entitled to have human emotions, feelings and doubt, and still be the wonderful person she was.
Perhaps it is scary to hear of such a seemingly faithful person question their faith. If they can have doubt, then what about the likes of us? If she could wonder about God's existence, then what if she is right to wonder? What if, after all, there is no God? These are the unasked questions at the root of this response from the revelations from MT, I believe.