In before OP asks why didn't his Susanoo become the SO6P.I suggest you re-reading the manga again. Long story short, he used his Susano'o as a vessel for the tailed beast chakras. Not his own body.
That's the reason I thinkI suggest you re-reading the manga again. Long story short, he used his Susano'o as a vessel for the tailed beast chakras. Not his own body.