Originally Posted by
Reathyr
Basically Lordaeron/Undercity in Battle for Azeroth is a indefensible ruin, there is little left standing top side, and severe damage below, it's too far away from Quel'thalas (and probably behind enemy lines at the moment) or Kalimdor for the Horde to safely transport building materials, workers, and a large enough army to guard them that it doesn't make it worth to do it, the same goes for the Alliance, it's too far from the kingdoms in the south do it safely, that's why they seem to be focusing on Stromgarde and Gilneas, apparently attempting to push out in phases Stromgarde -> Gilneas -> Lordaeron? -> Alterac City?? -> Andorhal??? -> Stratholme????
So the thing is, the workers are probably engaged elsewhere at the moment, as are the armies, and reallocating them to rebuild Lordaeron/Undercity at the moment is a risk not worth taking, just because of the manpower required to do it safely.