> "Because it can be difficult and expensive to keep sesame in one part of a baking plant out of another, some companies began adding small amounts of sesame to products that didn't previously contain the ingredient to avoid liability and cost. FDA officials said that violated the spirit, but not the letter, of federal regulations."
It seems that they prefer the "may contain" wording:
> FDA officials acknowledged Tuesday that statements that a product “may contain” certain allergens “could be considered truthful and not misleading.”
As a consumer, I'd much rather know for sure if a food has something in it that could kill me in it. If companies really want add allergens to their products unnecessarily, disclose that unambiguously, and limit their pool of potential customers that seems better to me than companies just slapping on a label saying that the product might contain every possible deadly allergen and letting customers take their chances or avoid them entirely.