Been this way for 150 years. Farmer has 7 kids, let's say 1 die to a childhood disease, 2 become farmers themselves, one takes over the family farm, and the rest move to the big cities cause they can't find work...as technology progresses, those same farmers have fewer kids. So today, a farmer has 3 kids, 1 stays to be a farmer and 2 go to the cities cause you can't find work when the only things in town are a gas station, small diner and grocery store