Terrorism was the reason given for the initial escalation towards the Uighurs around 2014. There were several domestic terrorism incidents involving a handful of Uighurs around, the most notable (to me) being there was a car-fire/bomb in Tian'anmen Square late 2013 and a knife attack at Kunming Train station.
Wikipedia lists a steady stream of domestic terrorism incidents involving Uighurs [0]. It seems like the Chinese government only has one tool in their toolbox--control--so apparently their solution is to eliminate the entire ethnicity, although my prediction is that ultimately that will increase the amount of attacks, because now the entire population has a (concrete) grievance as opposed to a few radicalized ones.
[0] https://en.wikipedia.org/wiki/Terrorism_in_China#Chronology_...