Why did the Lady of Shallot die? Think about the knight in "Keats "La Belle Dame Sans Merci."
"The Lady of Shallot," had a curse put upon her which required her to live separate and isolated from the world. She could not look directly at the world, so she lived in a tower with a window. Through the use of a mirror, she would view the world, however, her real connection to the world was through what she heard.
She accepts her fate, more or less, until one day when she hears the voice of a man, who she determines to be a knight. He is Lancelot of Camelot. The lady falls in love with his beautiful voice, and what she can see through her mirror. She determines that it is time to leave her enclosure, taking charge of her life, curse or not.
She ventures in a boat, sailing toward Camelot, determined to see her love, Lancelot. She dies on the journey, due to the curse, and arrives in Camelot, dead. Lancelot looks upon her, however, and finds her beautiful.
Like the knight in "La Belle Dams Sans Merci," the lady pines for a love. The knight loves a mythical creature, a fairy's child, clearly, like the Lady's love of Lancelot, this love is unattainable.
He is imprisoned as well, because he would rather remain in the dreamworld in order to be close to his love. He surrenders his life like "The Lady of Shallot" for love. Tragic romantic heroes who sacrifice everything for love, and can't see the error in their choices.