The reason

why I threw this book out for everyone to write on.

Well. The reason would probably be that I'm a lazy, lazy, LAZY person and it would probably take me fifty odd years to finish even half of this book. So in order for this story to actually go anywhere, I had to make it a public piece.
Public meaning I retain all rights for it, but everyone can write on it.
Read the rules with special attention to rule 666!