I think the answer to this question comes most clearly at the assembly when Jack breaks off from Ralph and starts his own tribe, installing himself as chief. Ralph shouts...
“Because the rules are the only thing we’ve got!”
But Jack was shouting against him.
“Bollocks to the rules! We’re strong—we hunt! If there’s a beast, we’ll hunt it down! We’ll close in and beat and beat and beat—!”
He gave a wild whoop and leapt down to the pale sand. At once the platform was full of noise and excitement, scramblings, screams and laughter.
Fear has gripped the boys: they are all terrified of the beast, and of danger - though, ironically, not at all terrified of the prospect of never being rescued: it's only Piggy and Ralph who really understand that fear.
Ralph's insistence on the signal fire and on being rescued is rational, and, in fact, the best way to get them rescued. But it doesn't address the boys' fear of the beast.
Because Jack can hunt and kill pigs, he's in a position to claim he can better defend the boys against the beast. He's got violence on his side: he can "hunt it down! We’ll close in and beat and beat and beat—!”". He draws the boys together into a strong team of hunters.
And that's why Jack's tribe seems to provide more security against the beast - and reduce fear.
Jack's whole attitude in the novel is "CONQUER!" The boys feel secure with him as their leader because he seems so confident that they can hunt and kill anything that gets in their way. Jack plays on the boys' fears. The boys do not want to be told to stay away from the mountain because there is a beast. They are afraid, and Jack convinces them that they can be stronger than anything.