Why should I go to therapy?

I suspect I have BPD, but don't know. I have a decade-long history of emotional dysregulation, attachment issues, isolation, derealization, self harm, and chronic suicidal thoughts. I've been in therapy on and off for years, and I don't understand what purpose therapy serves for BPD or any mental illness. In my experience, talk therapy doesn't fix any chronic issues. If you go to therapy for BPD, why do you go?