For me it comes down to nature and instinct. How have human beings survived for this long? What did our long ago ancestors do to feed their babies? My guess is that weaning was a long drawn out process not guided by calendars and clocks and employers etc. We are mammals, pure and simple. Things have changed a lot over time by way of technology and expectations of people but the fact that we are mammals hasn't changed. Plus there is all the stuff that has been scientifically researched, and the stuff that hasn't been discovered.