Personality disorders are not illnesses. They are the result of interrupted development and misperceptions about how the world works.
Many take no meds because symptoms tend to be reactionary and not something to medicate. Treatment with therapy helps a person to examine and rework their perceptions that cause the reationary distress that is very intense and very difficult. Unfortunately it can be hard for a person with BPD to enter into therapy or stay with it because of their mistrust of others and their intense internal experience of others, and of themselves.