Answer:
One reason that people may desire to migrate away from metropolitan areas is an overcrowding population.
Step-by-step explanation:
While living in a metropolitan area has many benefits (career and education opportunities for example) most people end up leaving because the busy atmosphere isn't for them. Whether there is a lack of sanitation from overcrowding, noise at all hours of the night, or the size of the population isn't desirable.
I'm also going to assume this is for AP Human Geography, a test I took a few years ago and passed :)