And thats just it right there: get 'er done quick. I mean, because so much of the movies are CGI, I get the impression that he wanted to get these things over and done and cash in.
Truer than most realize -- He openly said in interviews that the Star Wars movies were solely made to fund for future projects.
What I don't get is why Lucas would allow teams of creative minds get together and create more and more expansions of his universe, and then NOT use the brilliant material they came up with come filming time... you'd think having so much stuff already deliberated upon and decided (and also all of the EU material was checked and approved by Lucas himself) that that material wouldn't be ignored in the films. I mean, at it's basest level, ignoring said material is just costly and time-consuming...
As someone said before, Lucas is brilliant at creating an overall concept or idea, but the directing and script-writing, and even the novels, would have probably been more satisfying to the masses had they been given to abler hands. The novels already /have/ been given to other people, and they are probably now thinking "what the hell? -- George just made my certified expansion completely invalid?!?!"