>>1315
I mean he didn't like the notion of a cortosis weave alloy, a solid metal that could stop or disrupt a lightsaber blade, ever appearing on screen. Lucas was adamant that only lightsabers or something projecting raw energy in a similar manner (magnapulse staves) could resist lightsaber blades.
When the animators were working on the Clone Wars show and George saw Prae Visla dueling with a vibrosword, Lucas basically went, "What the fuck is this?" When somebody, dunno if it was Filoni or somebody else, explained to him the concept of cortosis and other lightsaber resistant alloys, he got red in the face and said, "No, that's stupid. Change it. Only lightsabers block lightsabers." Because they were already so far ahead in the episode and didn't know how to justify Visla having a real lightsaber, Lucas introduced the darksaber as an ancient prototypical lightsaber to serve as a compromise.
I could be wrong, but I would think that most Star Wars fans would cope better with having to hit up Wookiepedia to learn about cortosis or phrik than with something as corny as a "darksaber."
As another example, Mandalorian Iron was retconned pretty much by George Lucas' fiat as soon as he learned that it existed when going over a novel. It was just something that had escaped his notice when it was introduced years before.