The fracture happened before they discovered the gommage. In the game, at some point, they literally say that the first expeditions were to save people Who weren't in lumiere at the moment of the fracture.
In fact this event more or less destroyed many cities by putting the world intro Chaos with nevrons who roamed around the world.
They wanted to find as many survivors as possibile.
Lumiere Is like a safe place because It became an island with the fracture. Or something likes that.
