The ones who are managing this underground world, this world of humanity, are the most aware of how much longer it can last.
At that time, after Xu Xin and Xu Ying sent everyone underground, they specifically chose a few people who already held high positions on the surface to implement centralized authority.
Rather than simply centralized authority, the state at that time might have resembled imperial power more.
In such chaotic times, imperial power was the most suitable system. During that perilous period, when the remaining humans had just arrived in the underground world, with everything needing to be rebuilt, who cared about your human rights, equality, or freedom.
Follow the arrangements; if you're disobedient, you die. It's that simple.
This system has persisted up until now, meaning that today's human rulers are basically from families that have passed down power over a millennium.
