Why are the healthier menus so insignificant and put aside?

Have you ever thought about this? You go to a restaurant or to the grocery store, and you see the healthier options like low calorie and low carb, less butter or something along those lines.
What I want to know is why those healthier options aren’t the main things we choose. The unhealthier things are always there at the restaurants, and there is this tiny section with the healthier things for people on a diet.
I don’t understand why the restaurant can’t cook with the healthier ingredients for all their food, instead of just a few dishes, and why the grocery store just doesn’t sell the low calorie or overall healthier versions.
Does that make sense? Why isn’t it so?