Quite true! Geographically, keep in mind it would be trivial to blockade South Korea from China, and South Korea has been invaded by a Chinese Puppet state in the somewhat recent past (North Korea), with which they are still technically at war.

It’s no ship yard in Seattle.

You can't count on industry in any state that's going to be a direct war participant and on or, these days, even kinda-close to, the front lines, anyway. Look at Ukraine, and they're arguably winning. That's how fucked-up your production capacity gets when you're more-or-less successfully repelling an invasion, let alone when you're plainly losing. The other day they had, what, 30% of their energy infrastructure damaged, by their own government's admission? And the only reason it hadn't happened sooner seems to be that Russia just hadn't decided to do it yet (not to overstate Russia's advantage—part of why they hadn't done it yet was probably that they have limited ability to restock their own weapons, so preferred to hold such weapons in reserve for a time). Plus all the bombed or captured factories, difficulty and danger getting inputs and workers to any surviving factories, et c.

> Japan and South Korea have active shipbuilders building immense container ships (Ever Given was built in Japan), and Europe dominates the cruise ship industry.

Cruise missiles have entered the chat

Besides, it's very nice in these scenarios to build your ships the same place that's sending cargo, so you don't have to risk an empty or low-priority cargo trip the wrong direction before you can load up with the good stuff.

Plus, governments change. The US could well end up on a different side of a conflict from some current allies, or those allies might remain neutral and so avoid behaving too-favorably to the US.