Well, not just water. Tibet is a high plateau overlooking the Chinese plains. It's an obvious entry point for a land invasion into the Chinese heartland. Xinjiang is a mountainous and desert region with a similar role.
I know why they're doing it, it's just cynical for the locals.
Similar story for Korea, if you're a great power, wouldn't you move the possible battle like a few hundreds of kilometers away from your capital? You would.
