Why would he open the epic in this way in the the Odyssey?

Homer opens The Odyssey with an invocation to the Muse to inspire and guide him in telling the story of Odysseus' journey. This sets the tone for the epic and emphasizes the importance of storytelling and divine inspiration in the narrative. By invoking the Muse, Homer establishes the epic as a work of poetry that draws on divine inspiration and sets the stage for the epic tale that follows.