One push factor may be a lack of health and education services in rural areas. For example, in the UK many small towns and villages lack a hospital or secondary school, meaning people have to travel in order to access healthcare or education. Therefore, by moving to a city, someone may increase their quality of life as they can access services more easily.
Another push factor may be low wages, in rural areas the wages that people earn are often much lower than those offered in a City. This means that someone may move from a rural area into a city in order to earn more money, leading to a better quality of life.