Vertical farms don't need to worry about pests, weeds or blights and they put the crops right by the users, in the city outskirts. So that seems like a major part of the answer.
Weeds, pests and blight cannot penetrate a sealed enclosure with a filtered, positive pressure air supply. A vertical farm would be a clean room and quite possibly not operated by humans at all, but by robots that don't have to go in and out and be decontaminated.