Ralph explains the boys defection to Jack as follows: "They're having fun."
He pits this "fun" against the responsible needs of their community, which means tending to the fire:
The fire's the most important thing. Without the fire we can't be rescued. I'd like to put on war-paint and be a savage. But we must keep the fire burning. The fire's the most important thing on the island.
Ralph, however, loses out to the primitive release of repressed desires that Jack represents. The younger boys want to have fun through the indulgence in war paint and savage antics that Jack offers. He gives the boys meat, something they desire, while Ralph and Piggy offer them only the deferred gratification of rescue and the less exciting task of tending the fire.
Jack represents Hitler and his appeal to people's atavistic, unconscious urges for supremacy and violence—what writer Thomas Wolfe called the primitive desires of mankind and described as usually being buried under a rock. (However, he states that in the 1930s, they were unleashed through waves of racism, triumphalism, and warfare.) Jack provides something similar to Hitler's torchlit night parades and ominous pounding boots. Ralph and Piggy represent the ordered, civilized world of Roosevelt and Churchill—the appeal of which is more elusive.