Oftentimes "ingredients" will be an incredibly long list. As someone that needs to pay attention to ingredients on food for a severe tree nut allergy, it's so so so much easier to quickly parse a two-item "contains" section than a 40 item "ingredients" section.

I've made mistakes on food that has _just_ "ingredients", missing entries while scanning at the grocery store.

Unfortunately, "contains" isn't required, and its location isn't always obvious. imo it should flatly be always required and always in a standardized layout/location (e.g. in a clear to read box).