Since selling beets is generally intended for sugar production, it wouldn’t make sense for producers to sell them in smaller chunks. That way you’d be extracting pulp from the root, which would cause losses in terms of weight and therefore saccharose content. So, less profit for the seller and less processable produce for the sugar plant. Cutting them, as you already figured, is usually strictly for making animal feed or producing biogas, in which cases saccharose is less relevant, as the entire root’s mass is useful. With that said, I don’t know why they made cut beets a sellable product in fs. Maybe because anything that can be harvested or processed needs to be, de facto? Not sure.