Think of it this way: Trads (or any other woman) who don't breastfeed their babies are setting them out to be different from Our Lord at the tender age of 1, 2, or 5 weeks old. If they can't imitate Our Lord at 5 weeks old, how can they hope to imitate Him later in life when it is so much more difficult?
How will the children understand how much Jesus loved His mother, when they aren't as bonded to their own mother, due to skipping breastfeeding which is known to create a strong bond between mother and child? Especially if the mother goes on to work outside the home, send children to public school, etc.
Religion doesn't happen in a vacuum. Nature is a foundation that grace builds upon.
How can we do God's will in difficult things when we can't even follow basic dictates of nature as God designed it?