Why doesn’t Ralph blow the conch to bring them back? (p. 92)...

At this point Jack has asserted his authority despite being guilty of hunting when the fire burned out. He was able to turn the tables on Ralph by hitting Piggy and manipulating the other boys by appealing to their baser instincts. Ralph knows he is losing the boys so he blows the conch as a last attempt to remind the boys that he is chief.