Chronic pain, and other chronic physical health issues just break you down. Constantly suffering, often times in ways invisible to others is just hell. People who haven't gone through it simply cannot understand or empathize with the reality of it.
While not at the core root of my problems, my psychiatric issues and suicidal ideation predates my physical health decline, it is a significant contributing factor to my desire to ctb. It is also one that cannot be fixed by current modern medicine. I've tried anything I could get my hands on to alleviate the pain and conditions and always end up right back where I started.
It saps the will to live.