The part I read, and maybe this was not the main article but in the notes, did explain why a psychoanalytically informed approach works with personality disorders. Overall people think it is because this approach (and there are many forms of it) generally focuses on characterological change, not just behavioral change.

But more specifically the idea is that in personality disorders the kinds of defenses seen are well explained by Object Relations, which holds that people internalize early relations as parts of their psychic structure and then later replay these early, usually dysfunctional relations. Since psychoanalytic approaches attend to what is played out between the client and therapist in terms of transference/countertransference, it is equipped to detect and then attend to these projections of early dysfunctional ways of acting and relating. That is very basic but the general idea of it.