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. (Generally speaking, such USSR-aligned leaders/movements, including the PLO, were not hardcore Islamists, but had a more complex ideology, mixing nationalism with some socialist elements, on top of religion.)
China is perhaps seen as not much different than the USSR was, overall, in those quarters. The new camps are possibly more worrisome, but the USSR also had gulags, internally deported Muslim minorities ([e.g. the Tatars](https://en.wikipedia.org/wiki/Deportation_of_the_Crimean_Tatars)) etc. 
And, finally, on this point, China actually manages to have better/closer relations with some Arab or Muslim countries that even the USSR didn't have. This includes the Saudi ballistic missile program, [built](https://edition.cnn.com/2021/12/23/politics/saudi-ballistic-missiles-china/index.html) by China. The same goes, to an even greater extent, for Pakistan.

* 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.

* Then, 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".

* And, generally speaking, Muslim countries are not shining beacons of democracy and human rights. So the leaders thereof may not be exactly excited by discussions of questionable policing practices when they sometimes do that themselves [on a lesser scale] to domestic political opponents, some minorities, etc.

* *Some* of those efforts like deradicalization camps in Saudi Arabia, [are](https://www.ipinst.org/wp-content/uploads/publications/a_new_approach_epub.pdf) even praised by the West. So Muslim countries slamming China too much on something that China claims is just that [deradicalization, but] on a grander scale might backfire domestically, too. (Speaking of which, the Saudis give [best tours](https://youtu.be/JupSK4odKWQ?t=28) of the latter.)


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Somewhat of a coda here: some answers have made a point on the distinction between incorporating and granting citizenship (China) vs. how Israel treats the non-citizen Palestinians. But citizenship in a one-party state means much less than in a more pluralistic democracy.

Think carefully though what a China-inspired solution to the Palestinian problem could look like: a one-party Likud state, with a pseudo-autonomy for the Palestinian territories that means even less in practice than the current setup: elections where Palestinians would just get to choose among a list of Likud-preselected candidates, etc.