A really, really big weapon that makes Ultima Weapon look like a child's toy is hidden somewhere in those ruins.
You find that out at some point in the 2.x MSQ somewhat early on at level 50.
The GCs are fighting because none of them want any of the others to be able to get access to it.
But they can't fight for real without breaking a tentative peace, so they staged some sort of war game to...solve nothing at all, because no one ever wins.
In other words, the lore for this is a joke that is a gaping, nonsensical plot hole in and of itself.
Yeah, pretty much. "Data! Go fetch before the others can because reasons!" That's all the lore we got for this.
Far as I could find, there's not even a smidgen of information on what that island is beyond "Look! More Allagan Ruins!". We don't even know why the data is there, or what it's about. Seriously.