Lightsabers are an old traditional weapon, it's like a samurai sword. They're old af, but you're still gonna carve someone up with one. Nowadays, you get better ones with the invention of super-steels and stuff. MAybe you could put a tazer attachment in the hilt so it stuns while it slices. Also the technological equilibrium idea fits. The idea of tech being so advanced, there isn't a huge amount of room for improvement. Tech still improves, but in more subtle ways. More like the difference between WW2 weapons and modern weapons. Same weapons just better. Also if you look at the tech of the Rakata, it's hard to imagine anything really advancing far beyond what they had invented, and that stuff was ancient. I think the starforge had been out of service for about 20000 years by the time Revan found it.
Which raises another idea. Maybe the SW tech is all based on old Rakata tech, and with the Rakata not inventing anything in 20000 years, that might be why tech progresses so slowly. The galaxy is using borrowed tech without having the same capacity for invention as the original designers.