Most cows fit into the Cluster B category. If these NPD/BPD/HPD cases actually sought therapy for their problems the pickins would be a lot more slim at these here farms.
Cluster Bs are notoriously resistant to treatment, and therapy rarely helps. Even if pushed into therapy, virtually all of our Cluster B cows would still be here.
Borderliners can, in less-severe cases, gain some ability to self-reflect and manage their own emotional states in therapy, but the difficulty in getting (and sticking with) that kind of therapy, from the rare professional who understands Borderliner drama and game-playing and is still willing to work with them, means most never get it. They do tend to mellow a bit with age, starting in their 30s, however.
Narcissists can't be helped because, in their minds, they are never wrong. They lack empathy, so they can't see others' points of view, or understand their feelings. They have wide mood swings, so they often get disgnosed as Bipolar (Russell Greer is an example), and may end up seeking help for snxiety or depression, but a therapist will never get to the core issue--which is their Narcissism.
Cluster Bs are broken in a profound way, and are essentially unfixable. It's pretty fucking tragic, when you think about it; as horrible and destructive as these people are, they didn't choose to be that way. Some interventions in childhood or early adolescence can help at-risk kids from developing a full-blown personality disorder, but you have to catch them as those behaviors and attitudes are emerging--and that just doesn't happen, most of the time.