Sedate lifestyles, too much choice of food, cars/public transport, tv/internet all a big factors
My mothers generation and before thought nothing of walking 2 miles to the shops (with small child by her side) Kids walked to school and played in the street after. Snacks weren't an option, 3 good meals a day. Even housework burned more calories (carpet sweeping, hand washing etc)
Many also breastfed 3/4 hourly, by the clock (as per guidelines)
Having done both (ff and ex bf) I can say mine ff like a bf baby, on demand, as and when they wanted it (a ff baby can go dosy when warm too, so getting them to take that little extra is no different for either
Our children need to be walking and running free, not stucj indoors in fear of the boogy man, if we want to stop the obesity rise. Fresh air, no snacks, nice basic foods (including fats and sugars)