Baka, we clearly see that madara use susanoo with his rinnegan it's in the chapters, and each uchiha has there abilities. For example itachi and sasuke are parents it's normal they got the same abilities amaterasu and tsukoyomi, shishi got another one the kotoamaterasu and obito the space time jutsu. The susanoo varies from their uses you clearly see that itachi sasuke susanoo are different and madara also. I think obito can use susanoo but have not find it nessesary to be use until now. In the battle between obito and naruto,bee,kakashi and gay he has not yet attack seriously he have use jinchuriki the mezo statue and only fade in the other dimension. Obito is not showing he's full power yet.