Answer: He noticed that the songs upset Odysseus.
When Odysseus is at the court of Alcinous, the king hosts a banquet and games in honor of his guest. At that banquet, the blind man Demodocus is invited, and he sings about the quarrel between Odysseus and Achilles at Troy. Although everyone seems to enjoy the song, Odysseus is upset because it brings painful memories of the past. The king notices this, and he decides to end the feast.