Why does calipso allow Odysseus to leave her island?

Calypso allows Odysseus to leave her island after Athene asks Zeus to tell Calyspo that if she doesnt allow Odysseus to leave her island that if she doesnt that Zeus will strike her with a thunderbolt and kill her as he is not a prisoner to her island and need to get home to be with Penelope (his wife). Zeus sends Hermes the messenger God to tell Calypso. Although Calypso is furious and doesnt want Odysseus to leave, she lets him because obviously she doesnt want to die so she helps him build a raft and gives him gifts for his journey home.