sorry I don't mean 3 sisters specifically, but in general the preference for corn is driven by economic reasons beyond machinery capability.

More complicated crops that don't harvest at the same time are still limited by other factors like soil quality and nutrient availability as well - whilst those three crops specifically benefit being grown together, it's not necessarily more efficient (or suitable) in terms of land use across various crop types (although it's still better than just growing corn everywhere as a monocrop).