I'm guessing it's because they're already half-rotted when the season ends. Usually not a good thing in most growers minds.

Also, I've never understood why some people want all their carbon matter to break down that first fall, unless they plan on only farming the ground for 2 years. Maybe it takes 3-4-5 years, I don't know. Who cares? I can remember distinctly back in the late '60s, early '70s when moldboard plowing I'd see corn stalks roll over....but we were plowing BEAN STUBBLE! There was no gmo anything. Not sure the word was invented yet....but the stalks were 2 yrs old & they weren't deteriorated beyond recognition yet. But, 45 yrs later we're still farming the same dirt & I'm betting they're gone now. It may take a couple of years, but I'm guessing they all deteriorate on the same schedule once the plant matter has died, which normally happens to corn every year anyway. I don't think gmo corn turns into a biannual by some Monsanto miracle.