Three Goddesses

Greek mythology still has an effect on today's society; often, any series that contains the paranormal will have a episode based on Greek gods/goddesses, mainly goddesses, shows such as Charmed and Eastwick depict three main goddesses the first is an enterpertation of Athena, she would obviously be the character in the show that is the most intellegent of the three and she is typically the quitest, I believe that she is the quiet one because Athena is dipicted as being wise and there is a saying that those who are wise need not speak. The next goddess that is chosen is Aphrodite, this is played by the character in the show that is most associated with love, she is typically the single one in the show and may be portrayed as a bit of a loose woman. The third goddess that is chosen is actually a mixture of both Hera and Gaia, the resulting character will be the mother of the three and be married, therefore representing the aspects associated with Hera but the character typically is able to control nature they can make earthquakes, floods, and even send lightning. The question that I have though is why these three goddesses? Why not choose Artemis or Demeter?