Sad thing is, we do not actually need to be a world that is so stuck to certain areas.
If you look at each nation, and I mean like literally all of them, you could realize that most populated areas are populated because of bad planning.
That's the mistake by government, not anyone else.
Think as a person who live in rural area, you will love to move to urban area, either to satisfy your desire or seeking better job.
Think as an investor/businessman, you won't invest your money in rural area because it's lack of customers, rural area only good for certain businesses.