So I watched this music video, and this is in fact completely untrue. There are many scenes in which black/brown girls are casted.
One could conceivably argue that any white star who features twerking in a music video is automatically being exploitative.
However, that was not my perception of this video in particular. It actually appeared to me the director took pains to portray a variety of dance styles (ballet, interpretive dance, rhythmic gymnastics, break dancing, twerking, cheerleading, etc.) all as equally valid art forms. Every performing group in the video includes a variety of ethnicities. I think I did actually see a black/brown dancer in the ballet troupe, though it’s difficult to tell. Look in the rear left of this gif:
We don’t know if they cast individual dancers or hired a dance troupe, so if black women are underrepresented that might say more about the dance troupe’s selection practices than the video director’s casting practices.
All the styles of dance, ballet or otherwise are presented in the same fashion — talented professionals being brilliant + Taylor Swift being endearingly incompetent. The black women in the video aren’t portrayed as Taylor’s dancing accessories, but rather as experts in their style:
Moreover, at the end of the video there’s a sequence showing all the different professionals being silly and dancing in a non-choreographed manner, thereby humanizing them, showing they exist outside of their role as dancers in Taylor’s video:
I think if we interpret the twerking scenes in this video as demeaning, that says more about our cultural perception of black women than it does about this particular video’s specific portrayal of black women.