[protheus]

Besides the "social" part, there is the water one, groundwater must be under the maximum depth of you basement, or you'll be having a nonstop swimming pool under your house instead of a basement for storage.
The next one is the mountain relief, which means rocks to crack, instead of earth to dig, that means very high costs for every cubic feet digged. Besides this, the walls of the basement need to be made from concrete, again adds some more costs.