SF Writers aren't very good at sex. . .
Some writers can't write battle scenes, others can't write effectively about sex or political intrigue, I've found SF writers, as a group to be less than adequate when it comes to sexual activity (on paper, at least. I'm still waiting for that super hot female SF Writer with both poor eyesight and poor judgement to come along - If she could do stand up comedy as well, she'd be perfect).
It's really about each writer and their individual skills.