The reason farmers plant corn and not harvest it due to waiting for the corn to dry down in the field to avoid costly drying costs, because weather conditions can prevent harvest and because it's also sometimes uneconomical to harvest the corn due to low yield or because of market prices or because the corn is being left for livestock feed or other agricultural purposes.
The corn kernels also have to reach a certain dryness level to be harvested efficiently and if the corn is too wet, then farmers have to wait for it to dry on the stalk or pay for expensive artificial drying after harvest.
Or the ground may be to wet to support the heavy harvesting equipment which can cause soil compaction and damage the corn field and farmers may not have enough drying capacity or harvest equipment to handle the entire corn crop at once.
Standing corn can also provide natural ground, which helps keep moisture in the soil and prevents erosion and protects the soil over winter and some standing corn is intentionally left as a food source and habitat for migratory birds and other wildlife.
Also some countries have bans on importing of or growing specific types of corn, especially the GMO or genetically modified corn.
The country of Mexico has a ban on GMO corn for human consumption and many European countries also restrict or ban the cultivation of GMO corn and also Algeria also prohibits importing and cultivating of GMO corn.
Mexico banned GMO corn for human consumption, although Mexico still imports some GMO corn for animal feed.
And many member states have also opted out of growing GMO crops, though the EU as a whole has also approved several for important and animal feed and Algeria also prohibits the import and cultivation of GMO corn and even Bhutan also prohibits the import and cultivation of GMO corn.
The importation of the corn seeds for planting is prohibited in may countries as a result of quarantine and agricultural regulations and this also includes countries like China, Australia, Japan and even many in Asia and Africa.
Corn is also man made and does not exist naturally.
Corn is a man made crop and was domesticated from the wild grass called teosinte through thousands of years of selective breeding by indigenous people in Mexico.
Today's corn does not exist wildly in the wild and corn relies on human cultivation to survive.
Teosinte which is a grass is the wild ancestor of corn.
Ancient farmers around 9,000 years ago began to cultivate the teosinte.
The teosinte ears were also small, with only a few kernels far apart, unlike the corn we know and eat today.
And over many generations, farmers also bred teosinte plants with desirable traits, like larger ears with more kernels.
The process of the artificial selection also transformed the corn plant into a more useful and productive food source.
And modern corn is also a product of the long process of domestication and is a crop which cannot survive on it's own in the wild.