Because the whole idea of “black” and “white” is an arbitrary invention based on the very specific racial issues of the United States. For most of American history, there was a clear divide between extremely pale skinned English and Germanic settlers and the dark skinned sub-Saharan African slaves they imported.
If we go anywhere else, this dichotomy isn’t nearly as clear. Would southern Europeans like Italians, Greeks and Spaniards be considered white? Most people today would say yes. But if we actually look, they have more in common physically with Middle Eastern groups than British or Scandinavian groups. They aren’t clearly “white” or “black.” They’re a level of brown in the middle. Below are some Greeks, Italians, Spaniards, Tunisians, and Lebanese Arabs. Can you tell which are which? Who’s white? Who’s not?
Greek, Lebanese, Italian, Tunisian, Spanish by the way
The point is, arguing whether Near Eastern people like the Ancient Egyptians were white or black isn’t useful, because they, like most people, didn’t fit neatly into either category. The art and sculpture they left behind usually depicts themselves as looking similar to modern Egyptians. Their pictures of completely black skinned people were typically drawings of Kushites, who were actually sub-Saharan Africans, or rarer stylized paintings. That’s not to say there weren’t black Africans in Egypt, as there was constant contact between Egypt and Kush. A Kushite dynasty even conquered and occupied all of Egypt for over a century. But they weren’t the dominant ethnic group.