[ivi0nk3y]

You guys don't know how he got the Sharingan in the first place?

Kakashis team was sent on a mission and Rin, one of the three, got captured. Obito
(an Uchiha) decided to go save her while Kakashi carried on with the mission.
Kakashi had a change of heart and followed.
Eventually his eye got injured by the enemy while he was trying to save Obito.
Then Obito died trying to save Kakashi from a rockfall and he gave his Sharingan to Kakashi, who Rin transplanted for him, since Kakashi had already lost his eye.

Anyway, maybe Obito dying is the sacrifice needed for Kakashi to get his Mangekyou Sharingan.
Perhaps he needed to work on it a bit more or something while Naruto was away but yea.