Why did Escalus not sentence Romeo to death in keeping with his speech act 1?

In Act 1, Scene 1, Escalus threatens the Montagues and Capulets with death if there is more fighting in the streets of Verona. However, he does not actually sentence Romeo to death. This is not because he is being lenient or merciful. Escalus acknowledges Romeo's age and impulsiveness and decides to banish him from Verona instead of sentencing him to death, which is a far more severe punishment for a crime that is not premeditated. Banishment effectively ends Romeo's life in Verona, as he is forbidden from ever returning to the city.