It's because the Otaku (pervert) wants to know everything about his idol (whore). So the more info he has, the more he's satisfied. They write even the weight, height, zodiac sign etc Basically as much info as possible.

Online Otaku will compare notes or trade to find out more "facts" about their idol. The more of these you have, the more of a true fan you are, and fellow otaku will admire you.
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I hit her with the hammer on top of the head. She made a lot of noise and kept on making noise, so I hit her again.