I asked 4chan to explain MI to me, and someone said that Forge originally became available after you finish MI's single player.
">>617420684 (OP) 54-kun was a cyborg in a setting where AI's could become gods if they survived rampancy. He suffered his own form of rampancy, survived it, and thus ascended. And at the end of the universe, 54 stood poised to create his own universe, and Durandal was witness. But yeah its literally just a 'wow isn't that meta as fuck' before 'meta as fuck' was a genre like >>617421116 said. There's a reason you get access to the map tools after the campaign."
Is the part about map tools being available only after finishing campaign accurate? I didn't know that.