Why does Hemingway has the old man talk aloud to himself while he is in the boat?

Santiago realizes how alone he is after he leaves the boy Manolin. The rich have the luxury of a radio at sea:Santiago has only his own voice. Santiago once sung when he fished but now talking is enough,

He did not remember when he had first started to talk aloud when he was by himself... He had probably started to talk aloud, when alone, when the boy had left. But he did not remember.