Board Thread:Naruto Discussions/@comment-31196611-20180119183908/@comment-734582-20180119204052

The jinchuriki simply weren't really proper jinchuriki. The biju were sealed inside them, but also still sealed inside the Gedo, and the black rods gave Obito control over them. In essence, you could consider it an incredibly advanced puppet technique where both the Edo Tensei and Biju are puppets. Obito was the medium for the jinchuriki, the Gedo the medium for the biju.

Madara on the other hand, wanted total and proper control. And in order to do that, you need to be a living being. It's not totally clear, but it seems Edo Tensei had not revived him at full power. Either that, or as Edo Tensei he could not fully utilize his Rinnegan. Either way, Madara wasn't able to use his power in a proper way and hence needed to be revived properly.