Lord of the Rings is connected to Metal simply because the 'epicness' of the music really suits the story.
Take Blind Guardian's 'Time Stands Still' song from their album, Nightfall in Middle Earth. Its based on one of the best events from The Silmarillion, the battle between Fingolfin and Morgoth. The way Hansi sings, with emotion and that haunting chorus actually makes me visualise the entire scene.
Besides the fact that Blind Guardian are incredibly talented, Metal in general is the only genre that can do justice to an epic like LoTR.