When you haven't breastfeed your baby the entirety of their infancy the breast milk dries up. The mother can no longer breastfeed their baby because their body thinks that their baby is all grown up (or dead) because it hasn't been drinking the milk.

You can't just choose to breastfeed on a dime like that, you have to breastfeed from the beginning and continue on to keep up the milk supply. This is of course assuming you have sufficient capacity in the breasts to keep the baby alive in the first place, something not all women have these days.

I’m likely astounded some people are not aware that not every women can breastfeed their children

Breast feeding is not always possible, some women are unable to nurse for various reasons and in some rare cases babies can have an allergic reaction to things in their mother's breast milk (that makes it way in from the mother's diet). There are probably other reasons I'm not aware of that could be in play, too.

Some women just can't. I guess they didn't have cow milk or whatever either.

Otherwise, I guess feeding the baby cow milk is preferable to not eating?

Doesn't work like that friend.

Milk production might not start at all, it might start but ends unless used.