Why did Persephone have to stay in the underworld?

Persephone is the daughter of Demeter and she is the goddess of the corn, wheat and all things that grow on the land. Demeter controls the growth of everything that becomes our food and the food of all animals and she was an amazingly powerful goddess, her cult was mainly amongst women and still today she is remembered under many names by the pagan witches and those who follow the old paths. But back to Persephone. Persephone is the young daughter of Demeter, it is said that within her eyes can be seen the flight of beautiful birds, her hair is shinning and wonderful, she is the maid for ever young, forever beautiful. It is for this reason that she was kidnapped one day by Hades, the lord of the underworld and the brother of the chief of all gods and men Zeus. Now Hades stole her and carried her down into the earth where he looked after her and showered her with love. She became his queen. In the meantime Demeter (Persephone's mother and the goddess of the wheat, searched high and low for her daughter but could not find her. In her sorrow she forgot the land and the world became cold and the crops failed. Flowers died and people starved. If it was not for Zeus the whole race would have died, he alone new that Persephone had been taken to the underworld. In the end Demeter held Zeus to ransom and vowed that she would allow the world to perish unless Persephone was given back. In the end Zeus intervened and Persephone returned from the underworld and was reunited with Demeter. Hades however is a crafty God and he encouraged Persephone to eat the seeds of a pomegranate from the underworld. This act meant that for six months of the year Persephone has to return back to Hades and her mother Demeter once again grieves and the land becomes barren. When Persephone returns the spring finally breaks once more and the sun whines and the crops ripen. Even today it is hard to decide if the return of the spring is not the return of a beautiful maiden, one whose eyes reflect blue Sky's and delicate birds and who is scented with the delicate fragrance of wild flowers and who is reunited with the mother of the crops so that we may all live another year under the warmth of the sun. May the gods be blessed!