In Romeo & Juliet why does Juliet's family want her to marry Paris and not Romeo?

From the Capulet's point of view there are good reasons why they want Juliet to marry Paris and not Romeo. The principal reason is that they know absolutely nothing about the relationship between Romeo and Juliet. In an example of dramatic irony, only the audience and three other characters (Friar Lawrence, the Nurse and Balthasar) are aware that Romeo has married Juliet. Had they known, the Capulets probably would have attempted to have the marriage ended. After all, Romeo was a member of a family which had been at odds with the Capulets for many years and the feud between the two families often caused violence in the streets of Verona. Another reason they may have preferred Paris was because he was related to the Prince and that would have been a political advantage for Lord Capulet, though this is only a guess, because Shakespeare never offers much information about Paris, other than he is a Count (suggesting nobility) and a "kinsman" of Prince Escalus. Even though Lord Capulet speaks well of Romeo in Act I, Scene 5, it is doubtful he would have approved a marriage between a Montague and his daughter. His angry outburst at the end of Act III shows that he could be quite temperamental and news of a secret marriage might have caused him to become even more enraged.