Serfdom existed to prevent peasants from leaving those farms, people wanted to move to cities were wages and jobs were better but nobility wanted to force them to stay on those farms.
Serfdom existed as a step above slavery. The city may have been better for serfs but for the free farmer (if any) the farm was better. There is a lot of 'grass is greener' in the idea that the city was better for many farmers and so they may not have liked what the city was really like.