They would if they could. Most other nations are nowhere near the level of sophistication of China on 'making stuff'. It's not just cheap labour, it's a myriad of other things related to it that China specializes in.
China is not trying to take over the world, they just want to be the 'superpower' in their sphere, and to be the centre of their Universe.
Which is fine in some ways, problematic in others.
The list is long.
You need tons of people with tons of little bits of specialization, tons of factories run by experienced people, tons of workers for those factories willing to put up with rubbish, you need all the support: capitol, financial systems, export sophistication etc..
Surely, any group of people well enough organized could build maybe one such city of a few million people in ten years, but that's small.
In the meantime, in India, they can't get the electricity grid to work. Factories? No way.
Which is why we see a lot of software outsourcing in India, factories in China.
For assembling Nike shoes or something, other parts of Asia might already start to make sense. But for real manufacturing of most things ... it's China for the foreseeable future.
Also...SK was for a long time a authoritarian American client state and being a neighbor of China and Japan was in no position to "dominate it's neighbours" even if it wanted to
It is not ethics however that is driving a wedge between the United States and China. It is China's efforts to solidify its power over the Asian Pacific seas (in)conveniently named the China Sea and their trade routes, their One Road foreign policy efforts, and China's efforts to remain outside of the international order while also participating in it (e.g. IP theft, etc).