I believe because so much of successful recovery relies on the person [B]believing[B] that what they are doing will work. Bringing in alternative literature would only serve to create self-doubt and people would start chasing what sounded good as opposed to what has actually worked (within the walls of that meeting). (I know this firsthand).
Additionally, if you know anything about gold mining, then you know there is a whole lot more dirt than gold. Speaking franking, most self-help recovery books are simply not good. There are a handful of very good ones, but the vast majority should be filed under fiction.