It's becasue human populations are concentrated in areas that are lacking proper resources.
Found at the lowest point of a large drainage area, these seasonal, marsh-like ponds collect and store water from rain and runoff. Unlike vernal pools, playas generally fill when temperatures are unsuitable for plant growth, and often the water is salty, alkali or both.
source- google
True. A theory arises from certain phenomena or scenarios out of observation in an effort to explain why they occur, though they are yet to be proven.
