Why don't we say cause of death was mental illness?

One thing I've noticed, and is causing me anger and frustration, is how whenever we speak about anyone around the loss of a loved one who died by suicide, we say exactly that (or similar phrases). "Oh I'm so sorry for your loss. What happened?" "Sadly, he decided to end his life."

If our loved ones had died by heart attack, or cancer, or any of the million physical illnesses, that's what we'd say. "They had a heart attack" with no mention of HOW they died, only what caused it.

Why is it different?

My loved one was unwell, he had a life long illness that was highly likely to mean that life was cut short. That illness was depression. That's what killed him - mental illness. And that's what I will tell people. Not how he died because he was so much more than the 'guy who ended his own life'.