Acquiring Information
Be it the higher realms or lower realms, technology was something that appeared just a while ago. That's also why it can barely make any difference for high-level cultivators. Usually, it was good for communication or for things like what Krune did in the labyrinth, the 3D map.
Of course, there were several other real-life applications like illumination, displays, systems to organize each organization, etc. Simply put, technology was pretty convenient, even though it helped little with combat. That being said, it didn't matter which City you went to, you would see technology everywhere.
However, this underground City was utterly devoid of any type of electronic equipment. The illumination that would usually be done by various kinds of technological items like lamps were nowhere to be seen. Instead, the City used a primitive way of illuminating the things inside, Limunous Beads!