Earlier quoted context omitted.
Another control on this is the Overall Allotment Quantity of sugar, which is the USDA-regulated quantity of sugar which can be sold in any year. If you have too much sugar to sell, you'll have to store it or dump it. This is to keep sugar's price high. https://en.wikipedia.org/wiki/Overall_Allotment_Quantity
That's an... interesting mechanism. I can't figure out what the goal is, aside from, as you said, keeping prices high (specifically for those two kinds of sugar, which seems extra weird) - is there another reasonable explanation?
The loans are based on a variety of factors and have a variety of goals from ensuring that family farms exist (and don't get gobbled by mega-farm corps) to ensuring that we grow certain kinds of crops in this country to ensuring we build better combines. It's very complicated and any 'narrative' that has a single cause or explanation is likely incorrect.