Why do we look different? If we look at elephants they have distinct features, but they aren’t unique in the same way a human is. We have so many genes which affect our appearance. This is for good reason, identifying one another is crucial. How else would I know my Mum? Or the person who did me a favour? Or the person who killed my friend? There are other means for sure; some animals use olfactory cues, while others rely on proximity assuming those around it are friendly. Humans almost entirely rely on how we look.
“Identity cues” differ between people but do not confer a survival advantage by being used for differentiation. These are things such as fingerprints or teeth. “Identity signals” are phenotypic traits which facilitate individual recognition and assist in animal survival. Facial traits show more variability than other parts of the body. Each aspect of a face is genetically combinable and so features are not corollated (blue eyes doesn’t necessitate blonde hair), and this allows for more configurations.