Why did Aeolus help Odysseus?

Aeolus, the Greek god of the wind, helped Odysseus to return home to Ithaca by putting the north, south and easterly winds in a bag, leaving only a westward wind to blow Odysseus and his men home. He did all this purely to annoy his brother, Poseidon, Greek god of the sea, who was his cousin. Aeolus told Odysseus never to open the bag, for the winds will be released. Odysseus had no intention to open the bag, but while he was sleeping, one of his crew did, thinking it was some sort of treasure, while Ithaca was in sight. The winds blew Odysseus far off course and closer to other dangers.