I might be 'tipping my hand' here, but I spent my high school years in and around the studios in Burbank, California and even though you hear a lot of squawking about 'personal privacy' from the stars/celebrities*, there has to be a basic human element of curiosity about these sites and stories.
Look at us as a group, fairly diverse bunch I'd venture to guess and yet, we're all brought together by fanfiction. Now, true we love the hot and sexy stories, what 'normal' person does not enjoy being turned-on? If they say otherwise, their lying. Like the old psychiatrist's joke: '95% of people masturbate, the rest are lying about it'.
Everyone who can read above a 5th grade level has probably read some kind of erotica in their lifetime, even if they deny ever doing so. it is human nature to be curious about sexuality wether it is one's own or other people's. Personally, if I were the subject of said writings, I'd have to read them just to get an idea of what people imagine and/or think of me as a person or 'celebrity'. Although, I admit finding it a little disturbing when someone wants to put another person into situations involving things like, beastiality, kiddie porn, ect. I know it's just a story, not real, but to each thine own, right? Just not my cup o' tea.
*I differentiate between 'stars' and 'celebrities' as there are those with class and talent, then there are those who will do anything to be seen and talked about. I leave it to those here to decide which specific individuals are which.