People don't usually trust "common sense" when it comes to labels and their health or lifestyle. A pack of spaghetti that's just made of durum semolina is still gonna be labeled Vegan, just in case. That's how it is, for peace of mind.

EDIT: And part of it is because large corporations or shared facilities often share equipment to make wildly different things. It is indeed possible that apples run across a gluten-dusted conveyor belt, somewhere.