They don't give a shit what happens to some other sect. Muslims are characterized by their insane religious zealotry; anyone who strays one millimeter away from their dogma is a subhuman infidel that deserves to be burned. That goes for even other Muslims who interpret some passages in the Quran differently from them. When they're not busy attacking the West or Israel, the assorted tribes are killing each other instead. Besides that, China is also a valuable business partner for the decadent and morally-bankrupt leadership, and that'll trump any sense of kinship they would have for the Uyghur by miles.