After the other boys steal into Ralph came in the night Piggy says "I thought they wanted the conch"(168). Why do you think the other boys don't take the conch?

 The conch simply does not mean anything to Jack and his followers anymore. It is a symbol of Ralph's leadership that is now dead. The conch stood for democracy, dignity, and civilized consensus. These ideas were the opposite of what Jack wanted. Jack was able to effectively connect Ralph, the conch and Piggy with weakness. The conch only means something to Piggy. He cradles it and misinterprets its importance.