The USDA food pyramid favored grains because that is what the US farming could produce in greatest quantity at the time it was developed, thanks to machine-assisted farming tasks. Grains had enormous combine harvesters that could be operated by one person and harvest the whole field within a day. Produce like tomatoes were limited by the number of Mexicans and Central Americans that could be admitted by the guest worker program and could carry filled harvest bags to the collection point, for a few weeks at the right time of year.
Now machine harvesting and factory-style farming has expanded to some fruits and vegetables, using things like hydroponic lettuce tracks, horizontal trunk-shakers, vertical limb-shakers, and flexible-fingered robot arms. Or even when hand-harvested, the human pickers can follow behind a processing rig that trims, washes, sorts, and packs right there while rolling over the field, and transports the product out via portable conveyor belt.
Cauliflower, muskmelons, lettuces, culinary herbs, cabbages, and tree nuts have all benefited from harvest mechanization. Farms can even, at minimum, use a fleet of golf-cart-like vehicles, so that human harvesters can gather the crop from a seated position, rather than, standing, stooped, or crouched, and allow the vehicle carry the weight of the produce, thus making each human harvester more productive, even when the harvest still requires hands, eyes, and blades.
The machines, of course, represent a hefty barrier to entry from the capital investment, and favor mega-agribusinesses. Farms that can't hire enough cheap transient laborers or buy the specialized machinery are priced out of the industry.
But it does bring cheaper lower-carbohydrate foods to the consumer in greater quantity.