Obesity is on the rise in a huge percentage of developed nations, and not just western ones. Even South Korea has seen a huge spike over the past decade - the amount of obese men /doubled/ between 2009 and 2019. It went up 3x in China between 1993 and 2015, and is on track to be over 20% by the end of the decade. Japan is increasing at a much slower rate, but it's still going up. 25% of people in India are overweight, with that number and morbid obesity numbers also increasing.

Basically every country sees obesity rise as the people gain access to the modern diet.

Typically, because less food is available in day-to-day life.

If I sold cigs on every street corner in a "skinny" country like Japan, how confident are you that I wouldn't create a smoking culture?

This is not a matter of motivation or discipline. Such thinking is short-sighted.