Simple -- they have a monopoly. If you want to trade their products you need to subscribe to their data. However, now that NYMEX is also listing softs (albeit with no volume) and they no longer have a total monopoly, and now that they're on ICE they are supposed to be lowering the fees (if I remember correctly it will be $55). The short answer is that they're greedy bastards -- they want to rob you on market data fees AND on fills in the pit....