Wheat combines are incredibly expensive and as seasonal as a device can get. But they are so much more efficient than a bunch of men with scythes that harvesting would be impossible on the scale that we do it without them.
The biggest disadvantage of fruit picking and veggie picking devices is that they breed the fruit and veggies to suit the harvester and packing equipment. American tomatoes are hard and flavorless things that only are barely pink, never the crimson of the juicy, delicious ones my grandmother used to grow. You cannot make any sort of decent gazpacho with them.
They have graded sugarcane fields to be really flat, and cane harvesting is done by machines these days in the US and Australia. Sugar is a simple chemical, so the quality of the crop does not suffer. Places where they used to grow sugar that could not be adapted to machines, like Hawaii, have been abandoned to sugar planting.
