I have reason for over fat and its happen with few people.
Less sleep
Pesticides and other chemicals in foods
Air conditioning and heating
Fewer smokers. Nicotine is an appetite suppressant.
Greater use of medications
Population changes
Older birth mothers, whose children are more prone to excess weight gain than the offspring of younger mothers.
Genetics
Higher body weight = greater fertility
Assortative mating
I suggest this thing are the main reason for the over fat.