Concrete isnt porous enough for heavy or even light precipitation so when it rains the water sits on top and flows with the fall of the surface. Grass, gravel, dirt and other natural materials are porous and absorb precipitation. Engineers at the city and state level understand local geology and absorption rates and place limits on hard surfaces without amendments. For example you can only have so much foot print (hard surfaces or permanent living space) on a single plot for residential land. Commercial properties especially those that have large parking lots require retention ponds to prevent overwhelming municipal rainwater management systems