I don’t know about the mansions in the article, but my (limited) understanding is that the intention is to build cities that do get used, not to leave them empt

I don’t know about the mansions in the article, but my (limited) understanding is that the intention is to build cities that do get used, not to leave them empty forever, and that part of the reason is to help relieve population pressures on the larger cities like Beijing and Shanghai. They just sometimes build entire cities before anyone moves in, unlike they way cities develop elsewhere, little by little as people move in.