It's because the Black Zetsu part of him is what has kept him alive. If I had a pacemaker (no I'm not 80) that kept me alive, if it started to shock me, I wouldn't rip the thing off, would you?
Because of he did he would have to start using the bathroom and he doesn't want to do that. I mean if you were obito would you want to start learning how to poop and wipe again?