For a number of reason. It is easy to defend against "the beast" or other potential enemies and it is his headquarters, where he is incontrol . He sees it as a clean break with the rules that were made and meetings that took place on the platform and perhaps more importantly as a place untainted by Ralph's leadership.
Jack and his tribe make their headquarters at the Castle Rock.
They do this when they all enter Castle Rock.
Castle Rock
Jack is feeling guilty just as Ralph and Piggy are.
Jack leaves for Castle Rock first when he forms his own tribe and has to defend himself from Ralph's tribe.
Ralph fights with Jack. (epic)
Jack views Castle Rock as a strategic location for defense and as a symbol of power and control. He wants to establish his authority there and use it as a base for hunting and governing the group of boys. Castle Rock represents Jack's desire for dominance and control over the others.
He wishes to remind Jack and his tribe that they are really just English schoolboys and not a tribe of murderous savages.
To find out where the beast is. They think it must be at castle rock because that is the only place that Jack and his hunters have not hunted before.
Jack feels a mix of excitement and anticipation as he and the three others trot toward Castle Rock. The thrill of adventure propels him forward, while a sense of camaraderie with his companions strengthens his resolve. The unknown future that awaits at Castle Rock adds an element of mystery to their journey.
"castle rock" the rock outcropping at one end of the island
Castle Rock in "Lord of the Flies" represents the boys' descent into savagery and loss of civilization. It becomes a symbol of power, violence, and the breakdown of societal norms as it is taken over by Jack and his tribe. The progression of actions at Castle Rock showcases the boys' transformation from orderly society to chaos and anarchy.