Originally Posted by
LystAP
Considering that the Allagans had access to spaceships, I presume that there were originally guards and workers up there. However, when Xande forced Dalamud to send ALL of its collected energy down into the Crystal Tower, something that I do not believe either systems were designed to do in a hurry, it may have killed a substantial, if not all of the garrison up there. Additionally, even if a few survived, Dalamud doesn't seem to have a means of supplying itself, and the survivors may have left for the surface to scavenge what little they could.
With the vast core of the Empire destroyed and the Crystal Tower (that was the primary means of using Dalamud) nowhere to be found, it was essentially just a big orbiting lump of unusable magitek. There was no reason for any survivors of the garrison to remain and given that the structure was in high orbit with plenty of defense systems (which they probably activated before they left), there was no immediate fear that anyone could misuse it.