Almost nobody replants their own corn. Almost all corn planted is an F1 hybrid, the first generation of a cross between two varieties. Subsequent generations

Almost nobody replants their own corn. Almost all corn planted is an F1 hybrid, the first generation of a cross between two varieties. Subsequent generations perform very much worse. This is a natural thing not an engineered thing, many plants on the first generation cross between two varieties perform much better. Most corn is also patent encumbered, but that is less of the reason. Soybeans are actually different and before all of the patented genetics people did sometimes replant their own grown seed.