'cause it holds better than carpet under the rain, lol.
Are you asking why they are aspahtl and not concrete, or why are they all made of concrete/asphalt?
I don't know how about over there, but here, asphalt is the only way to go (I live in Costa Rica, with an 8 month lasting heavy rainy season, and about 5-10 earthquakes a day), concrete cracks in a matter of days, rendering it unusable.