Board Thread:Theories and Speculation/@comment-34436338-20180123200352/@comment-26107879-20180209031052

Why?

Naruto couldn't because he can't heal everything. His arm is still gone for a reason. Healing Gai at all is an amazing feat. A guy turning to ash who destroyed his very being was healed almost entirely. An eye is such a small thing compared to a leg, and he healed the entire being. Gai probably does not have enough of what Naruto needs to heal the leg like he did with Kakashi.

Gai might not be able to handle Hashirama's DNA.

Gai would not allow Orochimaru to kill a clone to heal him.