Same argument. If there's a country that doesn't get tariffs, that country will very quickly become the leading global exporter to the US. It's the same thing for the "penguin island" that everyone mocked: if you put high tariffs on every place but penguin island, it will soon be Penguin Island Logistics Center.
Setting aside judgment of the tariff policy and the chaotic implementation, it does make sense to make them blanket actions. Much of the byzantine nature of our existing supply chains is due to gaming of international tariff policy.
If I post something from Denmark to Canada, they want to know the origin of the goods. If it's China, the China tariffs (if any) apply rather than the Denmark/EU ones.
If the declaration is incorrect, the goods can be siezed or returned.
Penguin Island is a nature preserve (the whole thing), no one is building anything.
Exporters in country A (with high tariffs on exports to USA) ship partially completed products to country B (with no/lower tariffs to USA), and then do some manufacturing step. Country B then exports completed products to USA.
China was doing this extensively via Mexico under the USMCA [2]. It's not a matter of debate.
[1] https://www.trade.gov/rules-origin-substantial-transformatio...