The trick is that you have to have the jedi's super powers basically. So to make a lightsaber better than a gun, you've got to have the ability to see slightly into the future, have superhuman reflexes and twitch speed. When you take those, you can combine it with a sword that can reflect bullets, and actually use that sword to be better than a gun. Without any of that, you're just getting shot a lot.
Meanwhile, if you know the other person has all of that, you'll want the same since just using a blaster isn't going to get the job done.
I've always wondered if they could turn their abilities into using a blaster and shooting plasma out of the air...but that seems like it would be a good deal tougher. Basically the difference between hitting or bunting a baseball pitch with a bat, vs. trying to hit the pitcher's ball with one you throw yourself.