For many of us we don't think about it because we've never been confronted with it (which is why I said, your privilege is showing - it is very privileged to not feel alienated by these everyday things). If you look at many films and the casting involved, very often, the default experience assumed of the audience is "white straight male". To the point where when there're main characters who don't fit into that group, it becomes a "non-mainstream" movie, because it's apparently expecting a lot to ask the audience to identify with a non-male, non-white, non-straight character.

I haven't been following this issue so I don't know whether Shyamalan is in charge of casting, but I do remember being rather peeved with Lady in the Water which quite brilliantly had a huge cast of minorities, but the main hero was still a white male. It's these little things which remind PoC that no matter how numerous we are, we still remain second-class and don't deserve stories of our own.

Thanks for not getting on the defensive and up in arms. It's probably an issue you've never had to think about before, so thanks for your good faith.