Why is Piggy's fall emphazised in Chapter 11 of Lord of the Flies?
The fall is symbolic of the fall of all vestiges of civilization. The vast drop to Piggy's death mirrors the decline of the schoolboys since their arrival on the island.
It is also a death of any hope that the boys had. Piggy believed in the good of a system, and did not like the war between Jack and Ralph. Jack wanted to live his life allowing his sadistic impulses the freedom to act, while Ralph wanted to enforce his vision of rule, structure, and civilization.
Piggy's fall brings an end to all of their ideas. They have finally and fully become savages.
Piggy's death is symbolic of the death of logic and reason, just as Simon's death is symbolic of the death of innocence on the island. With each death, the boys lose something vital to their connection to the life they had before being stranded on the island. They plunge deeper and deeper into bararic savagery.
It should also be notes that, in terms of literary development, this is the climatic moment of the novel. Piggy dies, and Ralph - the protagonist - is left alone and helpless. All things have turned against him and he must now avoid capture and death, just as the pig had to avoid the same.