Partly I think it's insecurity. I think the sheer grandness of what "Star Wars" became might intimidate the artist who crafted it. Rather than saying "I made this movie that became bigger than I ever imagined" he formed a narrative about his grand 'original vision' and the (plainly falsifiable) stories of "The Tragedy of Darth Vader." Adding "nooooooo" to ROTJ reinforces this story.

Also I think he's a tinkerer. I repeat again, I think the endless Special Editions are really neat. I think was Lucas does to them is cool, and I'm sure HE thinks it's cool. Pushing technology, tweaking the movies to make them cooler He probably thinks blue Hoth IS better.