You only want to breast feed to that age and slightly beyond if you are living in a “famine” situation and the food is limited and you want to give your child the best nutrition for their developing brain.
This is beacue if the SHTF the amount of fats and especially protein availble for consumption may go down and it is better for the mom to be feeding their children the fats and proteins in breast milk should the only food that is left is nothing but carb rich food that is not good for a developing kid.
Thus this sorta nursing is something that you only see in third world countries, which means we will see it in our country (by nessisity) soon......
My wife's grand mother had a baby that starved to death during the great depression. I ignorantly asked her, "why she didn't breast feed the child". Her answer should have been obvious to me, she said, "I was starving too and when you are starving the breast milk dries up".