Twilight fanaticism

A lady called the library one day, her voice a flutter with nervous anticipation: she had to be certain that the sequel to Stephenie Meyer's Twilight was on hold for her.

For those of you unaware of what exactly Twilight is, you've been living under a rock for the past year. I have emerged into the sunlight, and now you will too. Even though I have read the books, I was taken aback by the fervor of the twilighters, as the fans of this series about the love story of a vampire and a human are known. I became acquainted with this fanaticism firsthand when this breathless lady (who was older than me) called the library.

How did a young adult book about vampires and love become so big that grown women sigh over Edward, the vampire equivalent of Romeo? I haven't a clue, seeing as the type of books that deeply affect me are ones like C.S. Lewis' Till we Have Faces.