Why does the boys plan for rescue fail in Lord of the Flies?

The boys only had one plan for rescue, which was to keep a signal fire burning on the mountain top. Jack made the offer that his "hunters" would accept the responsibility of keeping the fire lit. Unfortunately, on the day that Ralph spotted a passing ship, Jack had decided that he need all of his hunters to effectively hunt a pig. As a result the fire was left untended and it went out. The ship passed by and the boys remained unrescued.