Because he's totally crazy and totally vile. He's the kinda guy who would pick through refuse for food. And that's what he''s like with people, sex, relationships, vengeance, and anything else. Who would have an easy time writing such an unstable character?

That's sort of the point, because our named villains - all but the shadowspawn and such - are people who are smart about their evilness. Many, like Demandred and Semirhage have methods beyond murder, and they haven't reached a point where they logically need to rip a whole bunch of people apart.

I always assumed that a lot of evil occurs off-screen (as it were) because RJ didn't have a lot of interest in those parts. I also assumed that his need to include information and progress his massive plot required him to cut to the heart of the matter. For a lot of writers, that sort of forced focus can be a blessing.

Still, this story has multiple instances of sexual assault - thinking about Moghedien's is chilling to me, and she's terrible. RJ goes beyond mere "nastiness" and gives us Forsaken who acted like mythological versions of Milosevich, Hitler, Stalin, Pol Pot, and more. Asmo sent his mom off to be eaten by Trollocs. This was after he had offensive artists crippled in cruelly-appropriate ways.

I think RJ just didn't find a good time and reason to give the readers a full scene of the kind of thing you're talking about. I find that the series, in general, gives us tantalizing glimpses of great moments and then cuts off (before we hear the Forsaken plan, before Semi asks Cabriana her questions, etc.).

For my part, though, I'm happy that we didn't get to see what happened with Fain and that woman. Would you want to read what occurred after he'd mentally injured her son? That moment where his thoughts were flipping between a desire to "kill 'Al Thor" and a desire to force a booty call? That would have been quite nasty. For other moments, the reader's mind gets to fill in the blanks - that often produces the best scares, IMO.