I think it’s more complicated than that. Farmers don’t want to keep their corn seed now that they use hybrids and the trade off of having GMOs and well bred soybeans is that you either have to pay for all of the R&D with the first (and last) bag you sell or you can have them agree to not regrow the seeds and space the costs out year after year.

There are drawbacks to this decision but that’s why they did it that way