Why does Obito only have 6 reanimated jinchuriki when he fights with Naruto and Bee,
He has extracted the Bijuus with one to seven tails but the former Jinchuuriki of the Ichibi - Gaara - is still alive.
Another reason is that he is controlling them using the Six Paths of Pain 


  an Outer Path technique that allows a Rinnegan user to manipulate up to six bodies as though they are their own. 


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