It's not work out or time but diet that makes people obese. They probably eat fast food, sugary drinks, packaged food a lot everyday instead of unprocessed food like meat, veg, fruits, nuts.
Edit: Poor people in India are thin and rich are fat, quite opposite, again due to diet. Indian poor can't afford fast food in chain restaurants daily, must cook which is cheaper.
Keep in mind that unlike in Europe in the US processed food is often cheaper than fresh vegetables, fruits and meats. I always thought the US would be "cheap" in terms of consumer prices compared to western europe but it was significantly more expensive to buy fresh produce in US supermarkets than in Germany or Austria.
On the other hand stuff like coca cola is cheaper.
$1 “any size” soda at McDonald’s up to 40oz where I live, with free refills. Most everyone I know spent a good amount of their teen and early adulthoods surviving off of cheap food - fast food is incredibly convenient and as cheap as a healthy “struggle” meal of staples without a long time in a kitchen which you may not really have.
Meat, veg, fruits and nuts are expensive - and they go bad. You simply can't always afford them and sometimes you can't actually buy fresh stuff.
You see, a fair amount of poor folks get paid once a month, and since there aren't a lot of little grocery stores nearby, folks wind up buying food once and hoping it lasts the month.
Poor folks don't always have steady electricity nor a refrigeration, either: Living without a fridge makes your diet go to crap pretty quickly.
Time is another luxury poor folks have issues with, which also makes diets go awry.
That study is definitely not broadly convincing in my opinion, but just want to point out that there is a ton of baseless speculation in this thread trying to explain the obesity/wealth relationship.
At some point, it's the obvious that no one is stating: the American style of life makes a lot of people lazy as fuck, and they just don't give a fuck about working on their waistlines.
Edit: Poor people in India are thin and rich are fat, quite opposite, again due to diet. Indian poor can't afford fast food in chain restaurants daily, must cook which is cheaper.