Well, maybe they just wanted an actress who would be moving and would do a good job portraying Mary. Maybe they didn't think she had to genetically fit the part.
honestly...
Why then go through the trouble of making the architecture, dresses and everything else reflect authentically the culture, reality and physical appearance of first century AD Israel?
They seem to go through extraordinary pains to make everything look authentic except the focus of the movie — the Mother of God. Why am I not surprised?!
And how did they determine what is a "good job portraying Mary is, save for pre-conceieved notions that are not biblical? Which begs the question, why make everything else biblically accurate?
The problem is that people believe what they see in the movies. The movies leave an impression that lasts as visual memory. You start adding artistic license to historical events and you are re-writing and distorting history. I could understand it if the movie is presented as a "docu-drama,", a re-enactment, but not if it is portrayed as a historical film.
Again, if the best actress was needed for the job, and raxce and ethnicity had no part in the selection or authenticity of the movie, why not pick a Chinese or a blond-blue-eyed one? I am sure there is plenty of good talent out there besides the Maori actress.