Cuz it was mentioned that IT does that. Along with putting everyone under genjutsu, it captures them and slowly turns them into white zetsus.How do you know that? Shin Jukai Kōtan can be his Mokuton tech or he controlled the Shinju tree with that Jutsu, so i admit i could be wrong too, but we will never know.
But Madara was still nerfed as JJ, he never used his Jutsu's... Only CT and look how big that was.
What if he used his full potential, how big would his Katon be, or what would his PS be like?
Sasuke is in my top 3 fav chars, but that other guy said he could beat JJ Madara easily. I disagreed with that