I understand what you are saying. I actually found out from my therapist recently that some therapists don't even tell their patients if they have a PD. These disorders tend to be pervasive, and not every patient is willing to accept such a diagnosis, much less do much about it.

I was in therapy for a good while before my therapist hinted to me that I had BPD. I was devastated that she hadn't told me earlier. But when I found out, I asked her to help me with treatment. On my own I even went through two bouts of DBT. I am now to the point where more recent psychiatrists and therapists say they see no BPD symptoms in me. (I was high-functioning to begin with.)

I believe patients should be told and asked if they want any treatment. But we need to realize, as the name says, that these symptoms have become part of their personality--and the patient has to be very motivated to make progress in changing. If we consider diagnoses such as antisocial PD, histrionic PD, and narcisstic personality PD especially, then I'm not sure such people generally have much motivation to change.