We really don't. The majority of desert is not sand. Only around 20% is sand, and around 3% consist of sand dunes. Transportation in deserts is complex due to t

We really don't. The majority of desert is not sand. Only around 20% is sand, and around 3% consist of sand dunes. Transportation in deserts is complex due to the rocky terrain that usually fills the rest of the desert. It is economically cheaper and easier to take beach and river sand. (Especially since some countries designate sand dunes as protected areas)