Because the latest study of Kennewick Man, and a 12,000 year old Mexican skeleton, show that race can't be defined by one or two facial features. And, as for why Kennewick Man could look "Ainu" or "Maori" yet still be American Indian? Well, American Indian DNA is not all East Asian; it's got a fair admixture of Eurasian Siberian. Maybe it's got Denisovan DNA in higher concentration than other ethnicities, which would vary widely in individual percentage from person to person.
So, "race" as an alleged biological reality, when focused on skin color and a couple of facial features, isn't that; it's a sociological construct.
That said, the clueless, the racialists, or others, will draw the opposite conclusions, for various reasons.
This is also why it's sad that, in the light of the Charleston shooting, our president, Dear Leader, still can't admit that he's not a "post-racial president." I mean, he has no more elections to win, no more possible perceptions of "angry black man" to hide.