There are a million reasons I could tell you. Catch me in person some time, in fact, and you'll be hard-pressed to avoid me telling you some of them, probably whether you've even asked or not! ;) In fact, maybe "Why I Work in Publishing" should become a regular feature on this blog.
But for now, as the simplest answer to that question, I'll point to this. Reviews like this--heartfelt responses from readers like this--are why I work in publishing, and specifically, why I work in children's/YA books. Because I get to help make books that carry this much power, for readers of every age. Because stories become a part of us and stay with us forever and shape the person we become in the world and the mark we choose to leave on it. Because the things a writer has to say, and the words s/he crafts, can become black marks on white paper (or the technological equivalent thereof) that just might make someone else want to become a better person. And I get to help make all of that happen.
Does there need to be any other reason?