Why does it seem like therapy doesn't work on them?

I know multiple people with mental health issues. Mostly PTSD, anxiety and depression. And most of the time when they've gotten therapy, they get better and learn better coping skills.

However, People with Borderline I've noticed can be in therapy for years and never really get better.

I posted about my one friend before, and anytime I hear about here nowadays, she only seems to be getting worse and worse.

I want to believe theres still some hope for them, but the evidence is pointing the other way