To add some context (and not to justify this in any way), they aren't licensing "corn". They're licensing some random corn that they genetically modified to have a protein for producing betacaratin, or something like that. It's not like they've patented a wild variety of corn.
When it gets really frustrating is if you plant your corn next to your neighbors corn and they cross pollonate (because it's corn. That's what it does.) And then you keep the seeds to plant next year. And then that's violating some license. It's like "I didn't ask for your stupid genetic modifications, and now you're going to charge me money for them?!"
further reading https://ohioline.osu.edu/factsheet/agf-153 https://www.agry.purdue.edu/ext/corn/news/articles.00/gmo_issues-000307.html https://royalsociety.org/topics-policy/projects/gm-plants/if-we-grow-gm-crops-will-they-cross-breed-with-other-plants/ https://civileats.com/2014/09/05/this-breeder-is-working-on-organic-ready-corn-that-blocks-gmo-contamination/