The breadbasket as the name implies, grows mostly cereal crops: wheat, corn, barely and not a cereal but diverse use: soy. There are small operations that do grow more traditional vegetables, but due to their labor intensive harvests and produces short shelf lives, they are not terribly profitable (without underpaid migrant workers located near large populations to consume or process the produce quickly). This in my opinion is why we see things like water intensive almonds, only being harvested in places like water scarce California. Labor cost is something vertical farms often treat as a given, which at least for most of our non-cereal produce production, it is not.