"Processing food is very profitable, much more profitable than growing it or selling it whole... The more you process food, the more money you make." -- Cooked
And for decades, no entrepreneurs have noticed these "high profits" in processing food, so no one new has entered the field to compete those profits away.
And as far as the second sentence goes, well, I'm going to start processing some cucumbers I grew today, and just keep on processing them for the next decade: boy, should I be rich by then!