As soon as you start doing that, you start cannibalizing the domestic market with other milk that is domestic quota, first of all, because you have to produce one of these products. The only place you end up with a surplus is if you have over-quota milk and you ship it--it ends up in skim milk powder, and butterfat ends up in stock, and it can be used only domestically.
So that butterfat would displace domestic butter, and that's why that levy or fee is there. It's to give everybody their fair share of the market, I guess. If the export market were still open, it would be a different scenario. But there is structural surplus there of skim milk powder that is going for animal feed and is at less than world price.