Why do you think people persistently, for years, keep choosing something that harmed their bodies?
Just because you can do something, doesn't make it a "just" for everyone:
• Without any training, one day I decided to put one foot in front of the other and keep going, and managed 42 km, a literal marathon in distance — but it's obvious that, even though I was walking, most people can't do that.
• When I was at university, I gamified my diet to be the lowest cost without feeling hungry, and in retrospect that was probably 1100 kcal/day and only even safe because it was limited to term time, and it's really obvious that most people can't do that.
• Concersely, when I was on antidepressants and did graze myself into obesity, there simply wasn't a part of my mind aware of what I was doing to myself. I've lost that weight, but the strech marks are still there a decade later.
Or if burgers were a thing you had to go to an illegal dealer for.