I don't believe you're reading it correctly. (IAAL). Yes, he had a license that allowed him to grow the crop, but that does not change the fact that Monsanto was suing him for patent infringement, not breach of contract.
Typically when you exceed the scope of your license, the appropriate cause of action if for infringement, not breach of contract. The idea is that all the license does is to grant permission to do x where it would otherwise be prohibited by law. X here is to grow a crop but not replant the seeds harvested from it. There is no need to go farther in the contract and prohibit replanting because the premise of the license agreement is that everything not covered by the agreement is already illegal ex ante.
Typically when you exceed the scope of your license, the appropriate cause of action if for infringement, not breach of contract. The idea is that all the license does is to grant permission to do x where it would otherwise be prohibited by law. X here is to grow a crop but not replant the seeds harvested from it. There is no need to go farther in the contract and prohibit replanting because the premise of the license agreement is that everything not covered by the agreement is already illegal ex ante.