Earlier quoted context omitted.
Placebo effect
It could also be something like https://en.wikipedia.org/wiki/Allergen_immunotherapy#Oral
Additionally, a general fault of immunotherapy for allergy is that we tend to present the allergen in a manner distinct from its biological presentation - e.g., oral presentation of inhaled allergens. Since we have different mucosa-associated lymphoid tissues throughout the body, and since they do react differently, generally you're not going to get a great response to oral administration of a non-oral allergen (e.g., something you'd normally inhale, like pollen).