how does the conch lose its power at the end of the chapter

By chapter 10 Ralph, Piggy, and the twins are alone. The rest of the boys have joined Jack. One night they are raided by Jack and Roger. Piggy thinks they were after the conch but Ralph knows better. The boys are no longer interested in the conch and what it symbolized. Jack and Roger only wanted to steal Piggy's glasses for the fire.