What reason does Nestor give for the difficulties the Achaeans has in their homecoming from Troy?

Nestor does not know what befell Odysseus; after Ilion (Troy) fell, Athena provoked a fight between the brothers Menelaos and Agamemnon and divided the Achaeans into two camps; those under command of the former left, while the latter stayed. Odysseus left, but he and his crew soon returned to please Agamemnon. Nestor and his crew made it back home, as did a few other groups, but many did not.