Here's why:
* Michael Myers is a human being: He is not a supernatural entity or a ghost. His motivation for killing is never fully explained, but he is portrayed as a human being with a severe mental disturbance.
* He is physically present: Throughout the movies, Michael Myers is physically present when he commits his murders. He stalks his victims, confronts them, and kills them directly.
While there are some supernatural elements in the Halloween franchise, Michael Myers's killing spree is primarily driven by his violent nature and his desire to kill.