Moms working with babies at their side

In the old days almost all moms worked in the presence of their babies and children. Why is that so rare today?

Old fashioned photos of mamas nursing their babies while working. One just got done working in the cotton fields, another was hulling berries.

http://www.mothering.com/jenniferjames/

Slideshow of modern moms working at mothering magazine:

http://www.mothering.com/interactive/cool_stuff/working_moms.html