The problem is that there is no
the problem.
Our foods are unhealthy (low nutritional value, even if they provide the calorie content necessary to live; vitamin and mineral deficiencies lead to poor health outcomes).
Our foods are often too high in calories (portion sizing, sugary drinks, "coffee" that's 90% sugar).
Our culture is increasingly sedentary (cars versus walking and biking, television and computers that are engaging and help people lose track of time idling away on the couch).
And plenty of other factors I'm not thinking of right now. You can't point to any one of these and say this is the problem. They're all problems and all need to be addressed. Educating people on the impact of food choices and health (not even obesity, all the other health impacts). Reconstructing cities without the need for a 30+ minute commute to work or a grocery store. Emphasizing community activities that get people out of their homes and away from their televisions and computers (harder right now with COVID restrictions). Discouraging (by some measure) restaurants from serving grossly unhealthy serving sizes.
Some of these are more feasible than others. We aren't going to rebuild cities any time soon. Public transportation is a political third rail. People in some regions enjoy aiming their trucks at cyclists (too many close encounters in GA for me to even want to use a bike lane in that state again). Others are more feasibly addressed though.