thats the merchant's risk, thats why he makes a profit on his capital investment in wholesale goods, and if he cant shift the goods, he can sell them to a shipper to sell them in another market where the prices are sufficient to offset the increased costs in shipping.
you sure SOUND like youre mad at the grower, since you blame them for the government programs which are designed to stabilize supply, as well as prices (thats the subsidy/allotment system) so you dont go hungry, and he doesnt lose his shirt.
you mischaracterized subsidies and allotments as "paying farmers to not grow crops" when in fact this is NOT what happens.
many crops require specialized equipment, such as combines, which are not easily reconfigured to harvest wheat, corn, soya and potatoes, further the exemplar crop (wheat) is a MULTISEASON crop, with some varieties planted for harvest in spring, some in summer, some in autumn, and some in winter. that bag of "all purpose" flour on the grocer's shelves does not contain "wheat" but rather, a blend of different wheats to give the desired consistency to your cakes, pastries, breads or pasta.
each different finished wheat product requires a different blend for the desired results, the plain vanilla "all purpose" flour that gam gam used, is a fair balance of all the components of flour, suitable for use in many (but definitely not ALL) applications.
wheat farming is not as simple as you believe, just as construction is not just nailing a few boards together to make a shanty.