Issue with the US Coast Guard doing that is well...
China could declare it an act of war and use it as a reason to invade Taiwan or attack something somewhere
China doesn't want to declare war; because they know they'd lose more than they stand to gain in any conflict, in the long run. Instead, they're just using the threat of war as a scare tactic, and pushing to see how much they can get away with before anyone tries to stand up for themselves. It was a sound strategy in retrospect; considering the fact that they employed it for decades without any notable push-back from anyone.
Now however? That particular gravy train, among many others, is coming to a halt; and the CCP know it. Which is why they've begun to lay the groundwork for China becoming yet another insular dictatorship; by shifting focus away from controlling the Chinese population with prosperity, and more towards controlling them with fear of the outside world.