Those seeds are also the "property" of Monsanto. If I understand it all correctly, farmers have to buy new seeds every year. Theoretically, if China nationalized its entire agricultural economy and subsidized the or industrialized the process of harvesting enough seeds for the next year, like really took extreme measures to ensure agricultural sovereignty then maybe in some number of years and likely economic tragedies if not famines, they could stabilize production. But if they start harvesting seeds, Monsanto will consider it a violation of their patent rights, stop selling China seeds and the industry will get crushed by the competitive forces of capitalism. Basically there's no way to change without incurring expenses that would tank the industry and even if the state stepped in to take drastic corrective measures they likely wouldn't be able to stave off dire consequences.