Because naturally, the first person in importance and existence is oneself.
So, prompted by in_the_blue: my thoughts on the first person point of view in fiction.
I have an odd relationship with these sorts of things. Fiction is fiction. It's all a device. It's all a way to convey a story and lock you, the reader, into the moment. Which is a fancy way of saying that I have no opinion on the point of view as a point of view and I often wonder why so many people get up in arms over this.
Divergent by Veronica Roth is in first person. We are told "I" and "we," etc., and that's the narrator/main character, Tris. But once the story gets going, as a reader, I am swept along and forget the point of view, the verb tense, and so forth because I'm lost in the story. When I read a third person point of view story, such as Emma by Jane Austen, the same thing happens. I forget how it's written and get caught up in what is going on. I forget half the words, except as they let me speed faster through the panorama in my mind. If I notice the framing for too long before getting sucked in, then there's a good chance you're doing it wrong. Equally half of my favorite books ever are in first person and the other half mostly in third. The book of poetry, naturally, doesn't count either way. :grins:
There is one thing that I'll admit is difficult to pull off as gracefully in first person—names. You're stuck with self-referential names and thus, Andrew and Natalie, the names of Tris's parents in Divergent, are only mentioned once each. I had to ransack the book to find them for fanficcing. Other than that, they are rightly referred to as Mom and Dad.
So there you have it, the bulk of my opinion on the first person. Though if you think about it, "the first shall be last..." and all that jazz.