[depletedgherkin]

I would say two other big factors are easier access to junk food, as well as more people adopting a sedentary lifestyle.

To the second point, a lot of people from my culture still eat the same portions of food that their ancestors did, while living in a very different lifestyle in the present day. Eating a whole plate of rice as part of a meal is necessary if you're a laborer who's farming or fishing all day, but you'll pack on weight if you eat the same diet as an office worker.