hypester nails a lot of points I was thinking of as well. Though the popular YA series still do include physical combat, so I wouldn't see a reason to exclude it entirely. The production cost of choices and branching storylines vs. the expected sales could be a big hurdle, until there's some major evolutionary step in storytelling technology
If a game is heavily focused on interpersonal relationships, and these tie into the game mechanics, they could become somewhat cheapened once players manage to dig up the formulas used to guide the story / relationships (compare to the Mass Effect 2 Suicide Mission flowchart). Though that's just my gut feeling.