In fact, the reason everyone inside the Wall agreed to come outside the Wall, even knowing full well that the outside is extremely dangerous, is actually very simple.
It's because the resources inside the Wall are no longer enough.
In truth, the resources inside the Wall are far less than what they currently know, and the resource problem is also far more serious than they imagine.
Because although the inside of the Wall looks like resources are everywhere, the truly useful ones make up less than a tenth, and within that tenth, eighty to ninety percent are concentrated in those great forbidden grounds and lesser forbidden grounds.
So right now, across the whole inside of the Wall, the resources they can actually use are extremely limited; of course, this "limited" is in terms of total quantity, but if divided up for individual use, it could still last several decades, even a hundred years or more.
