Because they, like every other nation on this planet are looking out for number one - themselves.
Until the nitwits in currently in charge get the memo that everyone else on the planet is playing king of the mountain, and that we are currently on top and as a result the target, our world will be much more dangerous than it was six month ago.
Personal opinion.
You said — “Because they, like every other nation on this planet are looking out for number one - themselves.”
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Yes, that’s certainly correct (in your understanding). Furthermore, China has wanted for a long time to make a large portion of International waters their own *private sea*. They’ve been aggressively trying to do this for a very long time. The U.S. keeps patrols going in these areas where China wants to make it their own “private domain” so that it’s *established* by the U.S. that these are *indeed* International waters...
Every nation but us. Our elected officials are just interested in selling us out.