It works, when designed well enough. The problem is how do you continue to support the above ground structures, if you aren’t as lucky as Chongqing geographically. You have to essentially plan not only all the weight of the structures of each underground level, but also above ground level. That takes lots of highly specialized engineering teams to figure out, which is a huge upfront investment.

Which brings another major problem: Cost. Creating underground structures requires massive mining rigs and blasting and getting rid of the material that comes out and constant review of any potential damage that does when further expanding the city out; all of that costs just so much money compared to normal buildings. If your goal is for-profit development, you’ll never break even.

And of course the most obvious problem, most humans are not mole people and do not want to be underground. Sun-deprivation and outdoors-deprivation have serious mental and physical health issues attached, which are not solved by artificial UV-producing lights or indoor plants.