Why does Shakespeare chose to omit the title character from the opening scene of Macbeth?

To be precise, Macbeth does not appear in the first two scenes of the play. But by the time he does appear, alongside his friend, comrade, and fellow Scottish noble Banquo, we have learned much about him. From the first scene, for example, we learn that the witches, who are clearly up to no good, plan to meet with Macbeth. In the second scene, we hear an account of a battle involving Macbeth, where he is revealed to be a brave and apparently loyal thane to the king, who he defends against a rebellion led by the traitor Macdonwald. We also learn that Macbeth is held in high esteem by King Duncan, who values him as a "valiant cousin" and a "worthy gentleman." We also see that Macbeth is to receive the title of Thane of Cawdor. The former thane, having joined the rebellion, is to be executed at Duncan's order. So even though Macbeth has not appeared on stage by the end of the second scene, we know much about him and his circumstances. Perhaps by waiting until the third scene to introduce the title character, Shakespeare intends to add to the sense in which Macbeth is affected by forces outside his control, especially the witches. It is also true that Duncan's admiration for Macbeth adds to the sense of treachery that accompanies Macbeth's assassination of the king later. Through the witches' incantations that "what's fair is foul/what's foul is fair, the first scene has often been described as setting the stage for the villainy and evil that pervade the entire play. So by leaving Macbeth out of the first two scenes, Shakespeare arguably adds to the depth of the plot.