I would hazard a guess, that for the poor living in developing countries, the food available would likely be a very limited range of (at least) party quite bland, simple foods such as bread, rice, fruit and veg.
My grandfather was a young boy in Greece during WWII and was the second son of a very poor, widowed, older mother of 4 children, in a country and town destroyed by several conflicts. The family ate bread, maybe 4 types fruit (whatever was on season, so probably the same one fruit for months), feta cheese and maybe 5 types of vegetables (again, seasonal). All very simply prepared, to be economical with fuel. That was it. Smaller range than many fussy children have (mine included).
Also, in those kinds of environments, the discipline culture tends to be different - children might be literally forced to eat, which in current Western societies is generally not advised. Immediate survival in those circumstances is too important to consider anything else. And, of course, like someone already mentioned, some children will always be too fussy to even be forced into eating, so they will just get sickly and die.
I don't know. It's a very emotional subject, isn't it? I feel guilty for DS's (4) fussiness, but I have now counted that he eats 14 veg and 16 fruit. But ONLY raw, NOT cooked or in any way processed. Doesn't like many types of "junk food" e.g. burgers or pizza (I'd love him to try - I've tried all that "making your own pizza with funny faces", but nada success), but will sometimes eat chicken nuggets, fish fingers or chips. He likes boiled and fried eggs, hummous, chili ryvita.. He will eat rice and pasta with pesto or tiny bit of tomato sauce, but NOTHING else mixed. And only one type of kids' strawberry yoghurt. Cheeses are a bit hit and miss, but he likes mild grated cheese, philly and loves Italian hard cheeses, but, again, NOT on top of bread, only possibly on top of pasta, but preferably separately. I think overall, his diet is pretty balanced, but he will not eat many hot meals or even sandwiches, so appears terrible. He just wants everything as unprocessed and separate as possible.
A whole carrot, a whole apple, a chunk of parmesan, a hunk of bread, a boiled egg, few stalks/leaves of chives.. that's probably going to be his lunch box next year 