I’m not educated on this in any way, but I’d assume it’s something to do with either soil nutrient depletion or pesticides. Or maybe crop inbreeding. (Is that even a thing?)
On the one hand, I’d not put it past corporations to simply replant the same crop over and over until the soil is ruined. On the other, I’d also not put it past corporations to switch to a cheaper pesticide that ended up damaging the product in the end.