If you want to be charitable, its silence can in part be explained by logistical difficulties. Reporters are free to cover China’s suppression of democracy in Hong Kong, for the time being at any rate, but cannot get near Xinjiang without taking extraordinary risks. With no footage of their suffering, millions can suffer unnoticed in the dark.

I think this is a key reason but as he goes on to say,most countries don't want to risk the financial benefits of keeping quiet. A shameful situation.