First, attribute it to either the vagaries of evolution or the design of whatever creator one believes in, human beings have a decidedly inefficient system of energy intake. Our bodies make use of only a portion of the food and liquid that we consume. The rest is cast off in the form of feces and urine.
Folks from the outside observing the tent cities and homeless camps almost always take note of the escalating piles of waste and often unfairly attribute this solely to the general “nastiness” of the camp residents themselves.
Absent utilities like EBMUD and Waste Management, we’d have to spend a good portion of our weeks figuring out how to dispose of the waste ourselves. The truth is, most of us would not know how to handle it, any more than the people in the homeless camps and tent cities do.