Rural life is dull, you have a limited social circle and limited access to culture. And you have few opportunities. People today still crowd into overpriced cities with poor living conditions, because they dream of 'making it', and they can't bear the thought of toiling away at agriculture (or at a lesser job).

In China, an entire generation has been uplifted out of poverty by voluntarily relocating off of farms and into manufacturing jobs, and it's been so successful that it's cited as a reason for the popularity of current authoritarian leadership.