So why wouldn't dropping even a small fraction of the materials they were using the build the wall on top of the hole, or at least build something confined to that area instead? If they honestly thought the wall could keep them out... well, I just don't understand the thought process there. Why waste thousands if not millions of times as much material as needed to construct the wall would they could have just clogged the portal? And even if they couldn't clog it with the same relative amount of metal as they wasted on the wall, they obviously had thousands if not millions of times as much material to make it even more hardcore.
It just seems odd to me.