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.