Because you suggest violating (ok, maybe a harsh term - let's say 'fiddling with') someone else's intellectual property? I mean, sure, if you miss the story - there's always fan art. Write some fanfic, draw an art - find a way to make a tribute to the author and show your love for the story in legal ways, without, you know, copypasting and reusing (=stealing?) whole parts of it. I'm not fully sure if it can be considered an actual crime - using someone else's creations the way you suggest, if it is for your personal purposes only, but it sure as hell sounds ethically wrong.