idk, i went from chugging coca cola and eating fast food almost every day, to only drinking sugar free soda with meals and most food being home cooked, and it honestly wasn’t that big of a change. Same thing goes for getting more exercise, most people can absolutely ditch the car most of the time and instead ride a bike.

I think it largely boils down to knowledge, people have completely wacky views on what is healthy and not, they never learned to cook for themselves, they don’t understand that a diet change has to be sustainable (crash diets don’t work and make you feel terrible), and they haven’t learned how to change habits like what you eat.

The upshot of it being a lack of knowledge is that we can just… inform people about it.
If home ed. and PE classes were improved kids wouldn’t grow up to view exercise as some miserable thing, they’d know how to cook tasty yet easy meals and thus have less reason to turn to junk food, and if we had information campaigns about the fact that electric bicycles exist we could get tons of people out of cars and onto bikes where they get some actual exercise and fresh air.