The higher the dimensional ladder that was climbed, the greater the resources needed, especially if you were using the greatest of techniques and spells in existence.
As the last of the soul crystals were vanishing, Rowan did not pause in his movements because he had anticipated such a thing as one of the likely results of copying the Supreme Circles, he already had a solution in place long ago, and his consciousness called up the three metallic books that he had gained from his sojourn into the future.