Health: Just from a quick search on milk allergy –
“Milk is one of the most common food allergens in children. Studies in several countries around the world show a prevalence of milk allergy in children in the first year of life of around 2% to 5%. Many children lose their hypersensitivity to milk by age 3, but some children remain allergic for a lifetime.”
So while you are correct that incidence is at 2% to 5%, it also says that it is one of the most common allergens in children.