After Kolivan was though to be killed by the Galra, Keith became the leader of the Blade Of Marmora. He didn't think that he would be able to be the leader Kolivan was, but he became a great leader and led everyone to many successful missions while helping Voltron with taking out their biggest enemy. He always believed that Kolivan was still alive when his body was never found, but as a leader, he couldn't just leave to search for him. So that is why he asked you to help him.