There are some Uyghurs who could flee the country...

I read one of the US-based Uyghur activists accounts of how she escaped China. Thought it was going to be a harrowing story of people smugglers and fake IDs but it turned out that the genocidal Chinese government just gave her a passport and she bought a plane ticket to the US.

Every genocide in history has created huge outflows of refugees trying to escape death. Xinjiang has a huge and relatively poorly patrolled border with several Islamic nations who would all be very sympathetic to their brothers and sisters getting murdered. Where are the mass refugee outflows? Nowhere.