Many people migrate to big cities for different reasons. Life in a big city is difficult and different than it was before.
It is true that a big city offers many opportunities but there are many more challenges. One has to compromise with limited space in big cities. Poor people are forced to live in unhygienic conditions. They may be earning more than what they earned in villages but they are unable to save money because of the higher cost of living in big cities.
They also face the problem of language if they are not comfortable with the mainstream language of the city. They are often subject to ridicule because of their distinct culture. They are unable to afford medical facilities and quality education.