Some points that are perhaps worth mentioning/adding here:

* Unlike Palestine, the Uyghurs are not recognized as a country by anyone; so there's "but they're just separatists we're dealing with" argument.

* China deftly oppresses the non-Turkic Muslims (Hui) [less](https://en.wikipedia.org/w/index.php?title=Hui_people&oldid=1182582287#Current_situation), so they can argue it's not all out anti-Muslim stuff they're doing.

* Not surprisingly then, the Muslims that have protested the situation in Xinjiang the most seem to be the Turks, at least at the [official](https://mfa.gov.tr/sc_-06_-uygur-turklerine-yonelik-agir-insan-haklari-ihlalleri-ve-abdurrehim-heyit-in-vefati-hk.en.mfa) level. (But Pan-Turkism is also viewed with suspicion by many Arabs, see [e.g. (p. vii)](https://www.usip.org/sites/default/files/resources/pwks1.pdf).)

* A good number of Arab countries allied themselves with the USSR for realpolitik reasons, despite the general anti-religious tack of the latter. China is perhaps seen as not much different than that, overall, in those quarters. The new camps are possibly more worrisome, but the USSR also had gulags, internally deported Muslim minorities ([e.g. the Tartars](https://en.wikipedia.org/wiki/Deportation_of_the_Crimean_Tatars)) etc. 

* There's not a huge amount of press freedom in the Muslim world, in general. Coupled with the censorship of info at the source (Xinjiang) there's probably not a lot that reaches the average Muslim in re Xinjiang. Call this the double censorship effect, if you like.

* Finally, there's the means. A police state, even Guantanamo like [images/footage](https://www.youtube.com/watch?v=gGYoeJ5U7cQ), is still less striking than bombs falling on buildings.

* Coupled with that, [there's](https://politics.stackexchange.com/questions/74781/what-do-muslim-countries-have-to-gain-from-visiting-xinjiang-at-the-invitation-o) the Chinese effort for guided-tours "come and see for yourselves".