According to the clues Duanmu Huai gathered from the memory of Devil King Ji'Er, this world currently seems to be controlled by a mysterious entity. If one was to liken it to a game, Duel City would be the game's core, while the entire continent created around Duel City is a large-scale MOD developed by the opponent using the game's core.
This explains the oddly developed civilization of the continent. After all, the materials used to create the MOD come from the game's library. As a "fighting game", Duel City is set in a near-future backdrop, so it's only natural to have elements like television.
Moreover, since melee weapons of various kinds appear in the game, these materials could be directly used... It's pretty much this kind of type.
Of course, if it was only this, the game's official operator would surely take measures to stop it. Unfortunately, it seems there is no "official operator" for the game at the moment, and it has been taken advantage of.