You used hold before calling scatter3. When you turn hold on, it basically "freezes" the properties of the axes from being automatically modified (by functions like scatter3, for example.) If no axes exists when you call hold, it creates one in the default 2-D view.
You can create an axes with a 3-D view using the view command then hold it (or vice versa; hold prevents the properties from being automatically modified, but you can explicitly modify them.)
