I think this advice was more about not giving the baby a known allergen because they are a baby and it could kill them and it could be difficult to even tell they are having a problem because babies are often crying for any number of reasons.

I'm not saying the advice is sound, just giving a perspective on what led to that advice. It's not about "they might develop an allergy so don't give it to them" it's "they may be allergic already and cause significant harm".