Combine harvesters are also designed to harvest wheat varieties that have been bred to be harvested with a combine and dependant on synthetic fertilizers and that require all biodiversity in the area to disappear. More nutritious and environmentally friendly wheat varieties have existed for most of human history, along with the knowledge to cultivate them and not deplete the soil or destroy the soil microflora, but they can't be harvested mechanically, so they're disappearing. Developing robots that enhance the action of humans (not replace them) is better in my opinion than forcing the loss of food biodiversity to fit one method of harvesting.