If you take each group of people in the New World to be an item, then the title is essentially saying "why didn't the various different groups of people in the New World invent the wheel" - it's trying to emphasize that each of group of people is actually being considered a singular entity. Whether or not this is actually grammatically correct, I don't know, though intuitively it seems quite reasonable to me (which is generally a good first approximation of grammatical accuracy for native speakers).
