The premise of the force doesn't lend itself to being sick-ass cool in combat, either. Lucas was gunning for 'spiritual, detached, beyond materialism'. A force user wouldn't be the flashy guy, the force user would be the one who watches the flashy guy waste their energy and then strike them down in one hit. The Sith wouldn't be much flashy either, being on the sidelines for so long, and even at their height should they be flashy *with* the force, or rather, flashy in arts *other* than the force - there is a difference. A sith wouldn't mind being a good sword-fighter or someone who could pummel you to death with their fists, but the lightsaber may be something they might even embrace.
Darth Vader had one because he was a fallen Jedi. Then somehow that translated to 'All Sith have Light-sabers, red ones'. Honestly I would just had made the lightsaber an impractical weapon - It's a glorified plasma cutter the Jedi lug around. The Sith wouldn't use it because it was a Jedi weapon and they needed something more practical.
But alas, then comes Darth Maul and he had TWO sabers IN ONE and it all went from there. Gotta have a lightsaber fight in every movie. A hundred jedi just swinging it around in one movie, then six duels in the next....