[[WMG: The Mall is the product of [[Webcomic/{{Homestuck}} John, Rose, Dave, and Jade]] creating a universe]]
All the Kids really wanted was to hang out, preferably in a big Mall to show Jade the world and they got it. That's why the Mall has 25% of it.

[[WMG: The Mall is actually a battlefield for the [[Franchise/{{Highlander}} Immortals]].]]
Due to the nature of the Mall being combat-based, it can only be a safe assumption that it was made specifically for the Gathering, since the most inventive and skilled Immortals have an advantage with the abundance of materials for improvised weapons.