It is kinda hard to hide something of that scale, in case a prominent member of the Chinese mining community such as Jihan Wu (or anyone else for that matter) is threatened with prison time. Something is going to leak out.

The governments know that, so they won't do anything like co-opting mining farms. They can't even contain some of their territories ... (HK protests, etc.)

PoW algo change is one of the last things to change, if it ever gets to that point.