I am gonna make some sweeping generalization (how could you not when speaking about 1.5 billion people) but here goes:
Not really, the Islamic world didn't care much about ISIS and the Syrian civil war, both of which killed and displaced millions of people. The only place where Muslims pay attention to regularly and express outrage is Palestine as far as I know. I mean yes some Arab newspaper may talk about Syria or ISIS now and then, even talk badly about it, but nothing that will make people go out to the streets like Israel/Palestine does. Muslims are much more sensitive to killings of Muslims by the West than by other empires (e.g Russia or China) since the West is perceived as a threat to their way of life and other empires aren't. Israel is part of the West in their eyes. I am quite confident that if it were Israel or the U.S running these camps we would've heard much more about it in the Muslim world.
Just your common or garden religious zealots then.
They're farther down the hierarchy of nation state needs than where you need to be to be in order to call out someone like China.
So they all shit on Israel because it's the only "local enough we could conceivably do something about it" problem they can all agree on.
The geography is also not a good explanation. The Mohammed Cartoons, which happened in Denmark, made Muslims go out to the streets all throughout the world.
My explanation for "why Israel" is another comment on this thread.
Realistically they are much better off being China's friend which in China's view means not criticizing China for anything.
Pakistani PM said it best last month about Xinjiang:
"Because of our extreme proximity and relationship with China, we actually accept the Chinese version."
It's pretty sad, but you can't really blame him either, they can't really afford to lose all the deals and propping up they get from China.
I would be happy to see more opposition from Islamic countries though.
1) One thing to keep in mind is that religion is usually only the backdrop for some geopolitical issues. Yes, ISIS was an Islamist movement, but it was first and foremost opportunists seizing a vacuum of power in Iraq, and the instability in Syria, to put themselves into power. When looked at through that lens, why would a Muslim in Morocco or Algeria or Indonesia care that much about ISIS? Does a Catholic in Rome feel intimately connected to violence in Mexico? Most of them thought ISIS were a bunch of assholes, but it wasn't happening in their backyard.
2) Another thing is again politics. It's good for Arab leaders to criticize Israel and blame it for their problems. (Most of them) don't need Israel for anything. They rely more in China. That's the same reason most Western countries are falling short of accusing China of genocide.
3) From a purely religious point of view, Jerusalem/Al-Quds is a very important religious site Islam. It's the direction they originally faced when they prayed (Mohammed moved it to Mecca later), and is the location from which Mohammed ascended to heaven in one of his visions. China has no religious value.