1. It's brilliant... well, it's not bad.
2. It's a great way of passing the time in-between Harry Potter books.
3. It contains a secret code that reveals the whereabouts of a hoard of pirate treasure.
4. It's on the National Curriculum Official Government Approved Reading List of Very Important Books. (OK, we lied, but you never know).
5. All your friends have read it and you don't want to be left out when they start saying stuff like, "Wow, that list on page seventy-five is SO funny!"
But most of all - because it's very, very silly!