Monsanto, a large corporation, has made a LOT of money selling proprietary seeds and insecticide to farmers all over the world. They have effectively cornered the market with over 90% of US corn and soybean seed coming from their products.
Monsanto has lobbied politicians, had former staff that ended up in the USDA and FDA and spent huge sums of money on campaign contributions to both parties to remain an industrial juggernaut.
GMOs are not labeled when they are present in food, so there is little awareness of the problem among consumers.