I can't think of any common vegetable that I can go to the woods and find, most have all been man made from other plants, many times poisonous plants such as the night shade family.
Everyone excepts a goldfish as a real fish, yet, if you take a perfect goldfish and try to raise babies, soon there will only be brown babies and no gold fish colored fish, only when man alters these fish will the common gold fish be produced. In Nature, the gold fish is easy prey, they are not a fast swimmer and predators see them no matter where they try to hide. It is the same with what we call vegetables, all of Nature seeks to destroy these unnatural plants.
On the other side, the fruit bearing trees and bushes live and live and can produce 100's of years in the wild unattended. The more modified they are, the more Nature sends predators of course!