johnriley wrote:
Viewfinder can be used without having to switch on camera; Long lenses handle better than trying to use a screen image; Pentaprism gives better view that does not lag with action shots; Tracking and panning easier; Easier to use viewfinder in very bright light; Much larger lens choice; More stable cameras for hand holding; More physical controls as opposed to dipping into menus; Faster response and less shutter lag; Larger batteries for more shots per charge; Better weather sealing......

and I'm sure lots of other reasons too. Hope that helps!