The metals needed to diffuse the energies of magic that were driving the Anu mad, were located deep underground. Even though they had advanced machinery and dug out great caverns, it took a lot of effort to mine and process enough of these metals to make a difference.
There were only a few hundred Anu, and most of them were scientists, not people who were used to getting their hands dirty. Being underground, surrounded by mining and noise, wasn’t appealing to them.
They decided they needed a workforce, someone to do the difficult work for them.