The primary limitation on the number of cultivators was the concentration of Spirit Power in the air. Although the concentration of Spirit Energy was continuously increasing outside, one must not forget how recently the floods had receded.
Even if the concentration of Spirit Energy in the air could satisfy the growth conditions of Heavenly Materials and Earthly Treasures, it hadn't been long since the waters had receded.
Therefore, at this time, the external environment simply did not meet the natural growth conditions for Heavenly Materials and Earthly Treasures. Naturally, the increasing concentration of Spirit Power in the air had nothing to do with those Heavenly Materials and Earthly Treasures.