For one thing, the cost to sharpen the blades would be prohibitive to have done, and doing it by yourself would require special skills that many don't have, not to mention the time involved. Another would be reel replacement costs.
If you actually look at how a combine works, it is totally different than what you are asking here. The combine uses a sickle bar cutter the length of its platform/header (wheat and bean header), and then the reel basket "combs" the crop matt into the feeder housing to be processed. The corn head is so different that it isn't even close to what you are asking.