I will give you my take on it, and you can construct your response as you wish.
In Chapter 5, Ralph attempts to get order back to a society he quickly sees is falling apart. He blows the conch to call a meeting in hopes of reinstating the rules. Jack, however, bullies his way to the front of the meeting and tries to grab the conch, and therefore control, of the group, but Ralph allows Piggy to speak instead.
Jack blows up and blows off the rules and takes most of the boys with him away from the meeting. Ralph sees he's lost control and is no longer effective, so he refuses to blow the conch again...because he fears if no one listens, then his leadership has ended.
He knows in his heart, though, that his leadership has already ended and that is why he no longer wants to be chief. Piggy is mostly worried about himself and what will happen to him if he doesn't have Ralph there as a buffer between he and Jack.