People didn't used to have to avoid carbs religiously to not be big fat whales. Back through about the 1980s people ate plenty of carbs as part of a balanced diet.
Maybe it's just expectations of being lean or having abs that have changed, the aesthetic has changed to leaner and with more muscle? I don't know, is it just that there is so much delicious food available now that people can't control themselves?
Or is there something in the water causing us to fatten up more efficiently ?
The masses weren't medicating themselves with food like they are now. There also wasn't entire television networks dedicated to 24 hour programming about Food. Food this Food that, Food Trucks, Food Festivals, Food competitions. Combine this with whatever reasons people have for self medicating themselves, factor in a sharp drop in inactivity, and a rise in pleasures of convenience, and you have a perfect recipe for a rapidly obese population.
I also want to point out that when I attended University in the 90's, our University (which was a large one) only had 5 food kiosks. You go into schools and post secondary institutions nowadays, and the kids have literally at least a dozen options to fatten themselves. Not to mention that on every street corner across from a school is a fast food restaurant now. Wouldn't be the least bit surprised that in the next 20 years we don't have 75% obesity levels in North America.