I have no idea where this "mega slut" idea stems from. I'm not sure that there are a lot of games where you can do that without being punished for it (let alone ones in which you actually play as a girl so you can actually become such a slut). But for the most part, people play erotic games in such a way as to access as much of their content as possible. If you play a Lesson of Passion game one way and get a certain ending, you're likely to replay the game to see what you have to do to get other endings. If becoming a "mega slut" just so happens to be the only way to experience as much of the game as possible, then players are more likely to play as a "mega slut."
I was going to write more on the subject, but I got some very upsetting news tonight. I might give more input if prompted.