Answer:
Because Achilles was necessary to make it possible for the Greeks to beat the Trojans.
Step-by-step explanation:
When reading "Agamemnon's Appeal to Achilles" and "The Arming of Patroclus," we can see that Achilles was a key player in the battle between Greeks and Trojans, and his presence was essential to determine who would win the war. The Greeks needed Achilles and for that potent, we can see in the texts, that the Greeks refer to him as being not only a great warrior, but one whom Zeus chose to be a champion. For this reason, when Achilles refuses to fight, the Greeks pray that Agamemnon would go after him and change his mind, since without him, the Greeks will not be able to win the battle.