"Nature doesn't operate on special nature-physics distinct from the physics of artificial systems."

Who said that is does?. You asked how could it not be possible to recreate, and pointed to our own general intelligence as evidence of existence. But the existence of a thing does not necessitate our ability to create that thing.

What if the conditions of nature and the universe over billions of years led to natural intelligence occurring in humans and that is the only way? This scenario is entirely possible, and answers your question of how could it not be possible. Along with an infinite other amount of explanations. Just because something has a chance at being possible doesn't mean that it HAS to be, or that we will ever achieve it.

One way of looking at it: it means there's a DAG of causation and you don't have access to the entire root set.

(I'm not advocating for that idea being true, but I don't think it can be dismissed on the grounds of not having a clear meaning.)

It has very advanced production tooling, several orders of magnitude more complex than we have.

We WILL get to there. But we are not close.

3D nanometer-scale lithography of arbitrary materials is pretty wild.