because venice is a very sophisticated happy place and then the location change ot an island which is rough and unsophisticated miirors the change in the story
Othello is one of two plays in which Shakespeare uses Venice as a setting, the other being The Merchant of Venice. In both cases, Shakespeare depicts a thriving commercial society in which the inhabitants pursue luxury and see the world in mercantile terms, as for example, when Iago says that he knows his own "price" in the play's first scene. In both plays, attention is brought to the integral function of outsiders in Venetian society; Venice needs Shylock's borrowable ducats and Othello's military prowess. Above all, Venice has a duke and a council of senators, but it has no king. Under these circumstances, the final authority is customary and written law, but as Shakespeare shows us, laws can be twisted by political leaders who lack royal blood and the divine right to rule. Thus the Duke in Othello appears willing to hear Brabantio's complaint against an unidentified "abuser" of his daughter, but when he learns that the transgressor is Othello, an individual whose talents are essential to the interests of the state, he bends the law on the Moor's behalf.