Why do you think Macbeth is so interested in learning about the future?
Wouldn't you be if you had run into three weird sisters in the woods who told you partial truths? He is to be Thane of Glames, Thane of Fife, and King thereafter. One he had already, the second title comes to him almost immediately after his encounter with them, and the third is his wildest dream. Of course, the sisters also tell Banquo that he will not be a King, but his children will be. This hinders Macbeth's dream of being and staying King. So, he suddenly becomes very interested in what the future holds and how to avoid those predictions (or at least the part about Banquo's children sitting on the throne) from coming true. Since his vision of the future is limited, this requires him to visit often the sisters and request their sight of the future. They intentionally mislead him for fun, and he thinks he is making decisions to secure his throne for many generations. Curiouser and curiouser!