Why is The Last Airbender full of white people?

Why did they cast primarily white actors for the feature film adaptation of Avatar: The Last Airbender? Despite their personal names I theorize that Waterbenders are Inuit or Eskimos, Firebenders are Mandarin or Japanese [Sun worshipers = Mayan or Aztec], Earthbenders are Southern Chinese (perhaps Guangdong), and Airbenders are Tibetan. The various names have Japanese, Korean, Chinese, and Indochinese origin. So, how do these ingredients equal Anglo-Saxon? Is it because it is an American film? I thought Hollywood matured past nonsense like this. This casting isn't even an ethnic mix of protagonists. And they only cast young Mr. Patel by default. Was it really that hard to find young Asian-American actors who also are willing to study martial arts for a big summer movie? I mean, there were more Asian voice actors in Kung-Fu Panda (That movie was superb by the way.) I understand that your race has nothing to do with behavior or individual personality, but I'm talking about this grevious are of casting as relates to the original work. I mean what if the Lord of the Rings was casted with all Asian or African Actors; no matter how wonderfully acted. Wouldn't that look a tad off?