You also have old chains with an identity crisis. 5 Guys is by no means a healthy option, but they don't try to be. They don't throw in healthy options with their regular greasy burgers, doubling their ingredients needs. They offer Burgers, Hotdogs, Fries, and Shakes. That's it. They aren't fuddling with 3 new chicken sandwiches every season and salad options.
My uncle owned a Hot dog/Ice Cream stand. It was perfect. We made everything extremely well. But as the years went on he added Soups, Pizza, More fried items, even fish. And the product took a hit because of it. If you're a fast food chain, local stand, or food truck.. you need to keep it simple. Have your awesome namesake item, and a few others. Make it to perfection. And that's it.