Doesn't have to be actually difficult to comply for them to do this. It just has to be more expensive to comply compared to the cost of adding the allergen and

Doesn't have to be actually difficult to comply for them to do this. It just has to be more expensive to comply compared to the cost of adding the allergen and the lost revenue from people who avoid due to the allergen. It's like an auto maker evaluating the cost of a recall compared with just paying out settlements. There's no morality or logic involved, it's just numbers.