I think I can almost see the... well, what passes for logic inside their mainstream brains. They want to instill the idea of a mother feeding her baby, (because that's what the shirt's for), but they can't show breastfeeding
for fear of offending the little mainstream minds of their customers, so they "have" to show the mother bottlefeeding instead. It's just an automatic substitution for them and they don't even think about the implications.
It sort of reminds me of a children's book from the 50's called The New Baby or something, that tells the story of a small child who is getting a new little sibling. All through the book, the mother is dressed in typical 50's style (dress, heels, make-up, hairdo, pearls ... oh, and don't forget the apron of course), and has a 16" waist. They show things like the delivery man delivering the crib
but even when they show the mother the day before she goes to the hospital, she still has a 16" waist. You simply could not show a picture of an obviously pregnant woman, especially in a children's book, even though it makes the whole book just not make sense at all.