The current theory is that, when people become too old to work, they are send out to the wasteland, on the long walk. It is during this thousand miles journey that they saw a clutter of drop pods from a far. When they reached the drop site hoping to find something to eat, they instead found three dude (one always pantless) trying to grow corn in a cave.
Ridden with cataract, the old ones mistaken the corn for gold and decide to join the dude in their adventure of farming, carving rocks, eating lunch and not going anywhere.
This is the only way to explain why the survivors won't leave their cave to follow the first friendly party visiting their home and come back to civilization.