Here is my answer:
A very important question. I believe knowing this answer helps us to not go back there.
My story... the bullet point version:
* Overeating simple carbs (bread, pasta, rice)
* Poor eating habits (all day survival on Venti Double Caramel Macchiatos, come home and eat for four then crash... rinse and repeat)
* Dislike of exercise and sweating (and eventually comorbidities that made it dangerous)
* Italian family = food is love
* Wartime mentality old school parents = clean your plate, no waste (after 18 it was all me)
* Fat genes (I'm assuming this one) but Pop was fat and died at 67 from it.