Why do you think the framers did not include more expressed powers

The Framers of the U.S. Constitution did not include more expressed powers because they wanted to prevent the abuse of power by one person (or a small group of people).  The Framers had been been a part of the American Revolution against British rule, and they wanted to ensure that a monarchy (or similar form of government) could not be established in the United States.  Many government powers in the Constitution are very vague and open to interpretation for this reason.  Also, the Framers had the insight to anticipate that as the country grew and changed, its needs would also change.  For this reason, they made the Constitution into a "living document".  This means that it can be changed only through an amendment process.