Cheap, calorically dense food is widely available and people are less physically active than they used to be. Still, people have lost weight counting calories at McDonald's. It's no fun to be responsible, so don't expect people are eager to follow your advice to eat less, drink less, stop smoking, or wear a condom. Tell them to eat a Tide pod, though, and they'll do it.

Physical activity has been falling since the start of the last century but obesity didn’t start climbing until the seventies. There is more to it than your simplistic explanation and solution.

Green Revolution[1] happened and food availability greatly increased. There is no need for more explanation than this.

1. https://en.wikipedia.org/wiki/Green_Revolution

It's interesting that that article doesn't mention obesity.

Saying that people are fat because they eat too much had became non-PC around 1990s from my recollection so I would not expect such a statement from any Wiki article in 2019.