If specifically a Filet-O-Fish, I have no idea, but that would be true even if you remove "at 7AM."

That said, I've never understood the particular obsession about eating certain foods only for specific meals (ditto the Americanism that dinner should be the big meal of the day; I preferred a big lunch and a lighter dinner.)

Of course, from a restaurant perspective and particularly a fast-food perspective, it makes sense because to have a bigger menu, you have to have more advance prep items and have more different things going on at once.