We focus on the plant. Often we forget about the environment. The environment where these plants are encouraged is modified considerably from raw nature. If the environment is allowed to sit and do its thing for a while, it will revert and most all our engineered plants will be choked out by natural vegetation.
True, but other organisms in the area are part of the enviroment. Thus the presence of humans changed the enviroment, thus changing selective pressures for the plants.