I went through a class many years ago that dealt with weapons, distance, and time. I don't remember a lot of the details, but I remember being very surprised at how quickly a knife user could close a short distance. Less time than it would take to draw a gun and shoot them. That's why the police treat a person with a knife as a deadly threat. Not only can they close the distance on an officer, but they can grab anyone around them and either injure them or use them as hostages. Jacob Blake, is an example.