Board Thread:Naruto Discussions/@comment-1872728-20180201032503/@comment-734582-20180201070742

He was dying. Gedo made him survive biju extraction, and Black Zetsu made him survive Rinne Tensei. Naruto restored him further, allowing him to live for a while longer. But he was going to die, and judging by Obito's actions, pretty soon too.