I don't know why Lucas didn't just reshoot the shot so that Han shoots second.

All He would have had to do was have a replica of the cantina set built, have a few Han/Greedo costumes made/taken out of storage, and then hired a guy who could have reasonably stood in for a young Harrison Ford to play Han (he could have always cut-and-pasted Ford's head onto the guy's body later, anyway). And then, during the reshoot, the guy could have made a realistic dodge away from Greedo's blasterfire, and then shot the scaly green bastard from under/over the table in self-defense.

I honestly don't know why Lucas didn't just do it -- and many of the other changes -- this way. It would have cost a couple thousand bucks or so to do (I can't see it costing much more than digitally twisting Han's body around in the original footage) and it would have look far better and seamless.

Lucas seems to like half-assing everything he does, though, even when he had the millions to do better.