In the battle inside the space created by Bahamut, Rowan had been able to capture the Throne of Primordial Chaos with the aid of Primordial Soul. This could be a valuable tool in the future, as in many ways, the Throne of Primordial Chaos was stronger than Rowan and could reach places he could not yet touch.
With this Throne, Rowan could rapidly grow his understanding of the power of Primordial Chaos, deepening his insight into the realm of Primordials and boosting his attainment into the realm of Destiny.
There was also the fact that this Throne was very valuable to Primordial Soul, allowing her to make extensive changes in Reality that the sliver of consciousness that she controlled was not able to.
From the point of view of Primordial Soul, using this Throne at this point was wasting something so valuable it could not be easily replaced, but Rowan had his reasons why he was willing to give up this advantage.
