Not everyone is interested in sex in a game, and some people are interested in pretending they want a story and then dropping off after the smut. To be completely honest each persons reasons for roleplaying may not completely mimic anothers. For me, I need story first and foremost. If there is no story, there is no game. I don't care about the sexual aspect, though I do require that it comes into play at some point. Not for my personal arousal, but for my betterment as a writer and dealing with situations that I might not personally deal with. Furthermore, I use the sexual aspect of a roleplay to see how well the characters do mesh. Sometimes a game can fall apart after the sex, because a character will completely change in personality from sex - and that just doesn't interst me. A night of sex shouldn't make a character hav a complete 180 in personality, that just seems really extreme.
To be honest, I get very little roleplays. But that is because I am very specific, and very straight forward with roleplay partners. I know what I like, after spending 17 years roleplaying - and I am not willing to completely sacrifice my wants just so I can have a game. I did that enough when I was younger, and now I just want to enjoy my games. So what if I only have 4 actively running games on BM? I want quality over quantity of games, and I want specifically what I am looking for. Sex is important as a spice, but I never make my games the sole focus of it. I also require that writers put a bit more thought into their posts - as I have a minimum requirement of 1 paragraph per character I am playing with/as. For me, the games that have aroused me are the ones that mentally challenged me to a level where I went "Oh Gods, I can't wait for another post." - One such game, is on another site, has been running for over a year... has over 15 pages... and the posts are always a minimum of 6 paragrapns. That is what gets me aroused in a game. Amazing detail, deep story, mental stimulation that makes me wiggle in my seat and go "Now THIS Is what I am talking about."
Of course, all of the arousal versus writing aspect for me is based around the fact that I am Sapiosexual. Which can be very hard to stimulate, I require deep conversation, sometimes hours of mental foreplay - just to figure out whether or not I want to have sex. Most guys just aren't up for that.