After taking back his powers from Kabuto, he said he also acquire kabuto's information and research on the zetsu's and how he mentions in the Pic below, he has personal information to gather from the zetsu's. He might of completed kabuto's research by having the zetsu's and realized there the best candidates for him, having the 1st hokages cell means he would have his powers, and being that zetsu never showed signs of getting old "inmortal?" He might of found the "Perfect Body"