OP, I had Pneumonia, at 40 and was told that if I had of been a smoker I would of died.
I worked with adults with disabilities and in End of life Care, I've also supported people with HIV.
I'd agree that we are fooled into thinking that if we satisfy enough "tick boxes", weight, eating habits, exercise, we are healthy, but the truth is that you can't state that, or fully predict what will happen.
From what I understand, Doctors can understand why someone died.
What they can't always explain is why someone is still surviving, a loose explanation is genetics, physiology and "the Human Spirit", but it's just that we don't have the full knowledge, yet.
My Mum should of passed away, multiple issues, we're from Native American background and living into your 90's, through ill health/malnutrition etc was the norm. Had she of dies a lot sooner, the Doctors could tell me why, how she's still alive, is met with "some people have strong resistance". Even at her age, she regrets making the decisions (carrying on smoking etc), that have taken up to five more years from her.
We don't expect our Parents to die, likewise our children, in the developed world, it does sometimes need help to process.