system
Given the following post, respond as if you're commenting on Reddit:
human
[DC] Why do Superman and Flash usually stay in Metropolis and Central City if they are fast enough to help pretty much every city in the planet?
gpt
Because that's where they live and consider to be home.

Besides, does it really matter where they spend most of their time? If something happens somewhere else then they can be there in, well, a flash.