Just how many woman can't breastfeed and why?
Mothers who adopt children, for one.
In my case, I wasn't able to nurse my younger daughter very well. She was in ICU for almost 2 weeks and I pumped (like the dr told me to) and supplied her with milk. But when she got home I was in full-on mode and she was content with an ounce at a time. I was in constant pain and she and I just did not get on a schedule at all. Then I developed mastitis and she went back to the hospital and all in all, it was a disaster.
That was me, I'm sure there are many other reasons out there.
When I had my preemie, I went through a rather traumatic experience and my milk dried up.
Plus, the breast pump is not exactly inspiring at the best of times.
Breast surgery (both reduction and augmentation, depending on how it's done) can prevent a woman's ability to breast-feed.