Another good question of yours most of us can't answer
Obito could take an eye back in exchange for ruined life prospects :devil:
He wasn't a medical nin, that's why.
He wasn't gonna just stick his hand in Kakashi's socket, take his eye out, then put it in his and go "Ohhh ma gurd ah can see."
Thats the idea lolDo you know how op he wold be if he took it back?
Long/Short range kamui and intangibility, and a susanno. Nobody would be able to beat him.