On the latest episode someone representing the supermarkets admitted they spend the thick end of £1.7bn on making sure unhealthy products were placed in exactly the parts of the shop that would encourage people to buy them, not to mention the packaging, advertising, engineering of the food to be the digestive equivalent of crack, obfuscating the labelling of food so you don't really know what's in it, lobbying the government so that none of the above gets regulated, hacking the phones, computers and workplaces of people campaigning on food health issues (allegedly), etc etc.
There's also the problem that the information people get on what is healthy and what the best forms of exercise and diet are can be a bit vague - last night they were talking about the healthy eating guides being 30 years old and pretty basic, GPs having had no training on nutrition and the government spending about £1 on health and nutrition education and guidance for every £250k the food industry is spending on pushing unhealthy products. And that's before you get to the completely unregulated industry of diet books and wankers on YouTube saying "Everything you've ever been told about being healthy is wrong! Buy my service instead"...
And of course the problem of businesses essentially targeting poor areas with 3 chicken shops for every man woman and child living there.
People DO need to take personal responsibility but if a society is interested in the outcome of the efforts of millions of people to do that and the information that would help them in their efforts, vs the huge amounts of resources being pumped into the opposite outcome, that society wants to stop taking a piece of wet celery to a gunfight