Spoiler: the answer is racism.
BuzzFeed invited five fashion show casting directors to talk about why almost every model we see walking down the runway are white. Some of their answers, like James Scully’s, won’t make you want to vomit: Scully’s conception of diversity is more meaningful than the common tokenism he calls out, though he seems more market- than ethics-driven. Inevitably, there are also the responses that will lead you screaming into the street.
My favorite (read: least favorite) is Barbara Nicoli’s lovely little explanation of why Asian women aren’t sexy:
It’s also true that, for example, Caucasians have a specific body type, black girls have a specific body shape, and Asian girls have a specific body shape. So I guess there are some collections where it’s more perfect for an Asian body shape because they are more flat and less sexy, in a way. Asians, they are not curvy, so to put an Asian [who's] very flat [with a] baby body shape in a show where normally the designer knows they love sexy, beautiful, curvy girls, it’s a bit of nonsense.
You can read the full article here.