I think Tibet still very much has Western imagination captured whereas Uyghar Muslims... do not. Even more cynical analysis, Xinjiang is fundamentally an exercise in reducing the real problem of Islamic radicalization and the non response from many countries (including Muslim ones) is that they are quietly observing to see if the experiment pays off. The danger of Xinjiang is that surveillance state + "vocational" reintegration camps might actually be a productive model that can be exported elsewhere.
>>dirtyi+(OP)
Xinjiang is also much larger population (21 million+) wise than Tibet (3 million+), along with the former having a much larger Han population, making restrictions much harder (and less appealing) to implement logistically.