Tbh I think one of the biggest contributors to children being fussy eaters is that we have too much choice.
If they won’t eat one thing there is always something they will because there are so many choices. Pasta/chips/potatoes/risotto/stir-fry and all those have variations of ingredients and sauces. You could do a four week meal plan and not eat the same thing twice.
But in other countries where they have a more specific diet e.g. in the Far East for instance where they eat a lot of rice and veg with specific sauces, or Asia where curried/spicy food is more common, not to mention poorer countries where ingredients and choices are extremely limited, children don’t have the option of deciding they don’t like this or that food.
Most children here are fussy because we allow them to be. And that’s not a criticism, as a parent it’s an instinct to feed your child, so if a child doesn’t want something then you have the option to give them something else, and something else, and on until you find something they’ll eat.
There absolutely are children who will go hungry rather than eat what they don’t like, I was one. But those children really are in the minority, but it’s just far too difficult to sit with a child who is crying because they don’t want x and want y instead.
As for children who will only eat e.g. crisps and biscuits, and one I saw on one of those hospital programmes once who would only eat chocolate buttons, 
children only develop those kinds of habits if you give them that stuff in the first place. That’s an entirely different animal from the child who will only eat chips or toast.