Diego Garcia is an island of exceptional strategic importance to the West. When it eventually gets granted to a client state of China, that will steadily degrade the effectiveness of bases there. I expect slower movement than the time the UK promised to protect the rights of Hong Kong citizens, but that is a matter of degree.
I am not aware of Denmark giving meaningful control of Greenland to China or Russia, nor or any plans to push the US out: therefore, while I think the principle is worth considering, I find it to be a small concern not worth angering allies over.
Does that answer your statement of confusion?