It's because there's an assumption that only European history and culture is interesting to audiences so they just ignore other cultures and do their weird inaccurate costumes and castings and call anyone who has criticism for it a racist or a snob.

It's so easy to dismiss people by calling them racist when you take their culture, histories and mythogies and do nothing to represent them correctly.

And before anyone comes for me, I still find it fucking weird that Martin Scorsese decided to cast a white man in the role of Bill Smith, when the real Bill Smith was native American. It is especially weird to me, because Bill Smith is the only good white man in the movie. I just don't understand the need to lie about his ethnicity.

I hate that movie with a passion, btw. For many, many, many reasons.