As far as I can tell, the reason other countries haven't built anything like this is that it doesn't make sense from a grid engineering perspective, and the mai

As far as I can tell, the reason other countries haven't built anything like this is that it doesn't make sense from a grid engineering perspective, and the main benefit of building such a high-voltage high-capacity line is the propaganda one of being able to claim it's world leading. The big problem is that the grid needs to have enough redundancy to stay up if a single generator or transmission line fails, so the big high-capacity single transmission lines that China builds can't actually be used at close to their nominal capacity. It probably wouldn't even work as a propaganda stunt in countries with a free press; if the Trump administration built something like this, I just know the NYT headlines would be about how it was a useless Trumpian folly and showed the perils of his disdain for experts.