Last year they also kept the jumbos and sold them to a potato chip producer. Smaller sweet potato farmers harvest everything and sell them according to size and grade, from #1's to canners, which are the small or oddly shaped, that will be cut and canned. They can't afford the waste.
You are correct though ... if people only realized.
Years ago, the Imperial Valley lettuce fields had a bumper crop. Good news for consumers? Not hardly.
The DISTRIBUTOR owners of the crop, since these crops are already sold before planting, were ‘harvesting’ every third head initially; that was later changed to every fourth head.
The farmer was still paid the contracted prices, and the produce companies stil owned what was left in the fields. Not even the farmer was legally allowed to pick a single head for their own kitchen use.
It all had to do with optimal control of price. Pick “too much”, and the income from those “extra” heads would drop the price just enough to not increase profit. Pick “too little”, and the false scarcity would drive prices too high to sell at an increased profit.
They have professionals who calculate this optimal profit/harvest down to the last pound practically, and that much and no more is picked; the rest is left to rot or to be plowed under; sometimes entire fields or orchards...but the farmer was still paid his base payment.
Same with any produce, be it onions, potatoes, or berries, or orchard fruits and nuts.
OTOH, small farmers, who do not deal with the major packers, have to sell any and all to whatever markets are available to them.