Why can you guys not understand Mangekyou Sharingan....Lecture time
Ok well think about it what requirements does the Susano'o have? For Sasuke and Itachi they both had to have Amaterasu and Tsukiyomi to unlock Susano'o. NOW Since Kakashi only has one eye he can't perform 2 Mangekyou Sharingan techniques therefore he can't access Susano'o. Furthermore not all Uchihas can use Amaterasu and Tsukiyomi only Sasuke and Itachi can since their family. Each Uchiha family has different abilities, Itachi and Sasuke have Amaterasu and Tsukiyomi, Shisui has Kotoamatsukami and Izanagi (remember Danzo had Shisui's other eye)
