I'm not a doctor but ---
I was a public health administrator for several years. Our target health issues were unplanned pregnancies, obesity, healthy diets, drugs, alcohol, smoking, exercise and oral health. All categories were what I consider Behavioral Health. So yeah, pretty much avoidable.
Some of the big ones that are considered standard of care practice in the U.S. are heart surgery and heart procedures (statistically a massive fail), statin medications ( a marketing ploy that generally does not extend life).
For most folks with high blood pressure and diabetes these can be reversed by going to a whole foods, non grain diet and losing weight.
So yeah, living a healthy lifestyle that includes plenty of whole foods and exercise goes a long way. The obesity epidemic is pretty much killing people.
This is not to say that a person that checks off all the healthy living boxes will not become very ill. It is just that in general they will live a fuller and longer life than their couch potato, potato chip chomping contemporaries.