The film was mostly made in New Zealand, and it was financed by an American Hollywood studio directed by a Kiwi with a Kiwi production crew. There are also several Australian actors in the film, Hugo Weaving, who plays Elrond, and Kate Blanchett, who plays Galadriel. They're both Australian, but again, they're doing British accents. So all the accents are British. Why? Well, I think it's because for an American audience or for an international audience, a British accent suggests a sort of otherness,. like an other worldliness.