Lel obito was almost dead and owned bz, while bz's will owned madara. You can't refute thatThe difference is BZ pierced the Hashirama face as well as most likely Madara's heart, not just outside the body and Kaguya fought from inside the Shinju to successfully possess him. Obito did not have the Shinju inside him, nor the Juubi when he was possessed, in other words it would be pointless for BZ to try anything further.