Nestor tells Telemachus that half the men left Troy and half stayed behind. Nestor left, but Odysseus stayed behind. Why did this happen?

Nestor tells them that after the sack of Troy the gods decided to make life hard for the Greeks. First, the Greeks held an assembly at sundown, which is wrong in itself, during which Agamemnon and Odysseus argued with each other in front of the troops. The forces split: half stayed in Troy, half left under Menelaus. When Menelaus' men stopped to make a sacrifice, Odysseus turned around with the Ithacan contingent to plead with Agamemnon. Nestor stops reminiscing and refers to news from Idomeneus in Crete that Agamemnon was killed by Aegisthus, who was in turn killed by Orestes. Telemachus states that he wishes he were as brave as Orestes and could exact that sort of revenge. Nestor has heard of what is going on with the suitors in Ithaca and he asks Telemachus whether or not the people side with him. He also mentions that Athena used to protect Odysseus and will probably also help Telemachus. He also expresses hope that Odysseus will return home and avenge himself.