Uighurs are one of 56 ethnic groups in China, according to the official framework. For a long period of time, Uighurs and ethnic minorities in general were permitted. They were celebrated as a form of a socialist multiculturalism, but really only certain permitted differences were allowed. Uighurs could perform their ethnic dances and they could dress in a particular way; that was fine. The ideology they practised, however, needed to be in line with the Communist ideology.
This began to change, I think, in the 1990s, when the central Asian republics came into being following the fall of the Soviet Union and Uighurs begin to talk again about having East Turkestan or Uighurstan, about having their own nation. Tibetans also came to the fore as wanting to have their own state.
China saw this development as an existential threat to the nation. They have a “one China” policy. Taiwan is also included in that policy as being among the threats to the nation. Breaking up the nation is seen as something that would be detrimental for the future.
In 2001, when the U.S. began the global war on terror following 9/11, China, instead of talking about Uighurs as separatists, began to talk about them as terrorists. That in turn amplified the threat of violence in the Chinese imaginary. Uighurs in general are seen as thieves, as violent, and Uighur men especially are seen as threatening. Addressing this is something that the Chinese nation as a whole and people in Chinese society have seen as important. They feel safer.