Why did populations concentrate in smaller areas during the agricultural revolution

Because an area of land could support up to 500 times' as many people by farming as it could by hunting and gathering.

During agricultural revolution, due to increasing pressure on local environment, the population began to increase in smaller areas.

Explanation:

An area of land can be used for growing crops instead of hunting and gathering. Because of the revolution in agriculture, human population has grown at an unprecedented rate.

Small areas of land can support as many as 500 people for farming and people didn't want to waste those lands with hunting. The food people consumed also changed a lot, as the farmers planted the seeds that contained desired qualities. This gave rise to domesticated plants which was quite different from the wild ancestors.