They built their tower, Walk-Brass aka Anumidium aka Numidium, but needed a stone to activate it. Their intent was to use the Heart of Lorkhan.
But the Heart is already the stone of another tower, Red Mountain.
Could it be that trying to have one stone serving two towers at once is, to use the technical metaphysical term, a Very Bad Idea?
If this theory isn't just BS (and it probably is), then this gets one to thinking what might have happened if Dagoth Ur had finished Akulakhan...