Here's what I get from the interview:
Lucas is a quiet, shy, introvert documentary filmmaker who is used to doing everything himself, therefore if things don't turn out exactly the way he wants them to, then he thinks something is wrong. Compromise is what a film is all about, Kurtz says so himself.
When SW came out, it was the right movie at the right time under the right circumstances. It became more successful than anyone could possibly have imagined. The success blindsided him, but he is lucky to have more control than most filmmakers do.
With the success and money that SW brought.....not to mention the stress (see Empire Of Dreams), Lucas decided that he was gonna hire people to do it his way while at the same time, set up and reorganize Lucasfilm and ILM to accomodate.
ESB turned out waaaaaaaaay better than Lucas had thought and he WAS NOT responsible for it. It was Kirshner, Jim Henson and those 3 writers who made ESB as good as it was. I think this scared Lucas.....other people doing it better than him would make him scared and defensive cuz his control of the whole thing was threatened.
After ESB, Raiders comes out and Lucas somehow becomes convinced that audiences just want a cheap thrill. So he's determined to make Jedi that way. Kutz disagrees and takes off. Also at the same time, Hollywood was coming down on Lucas (see Empire Of Dreams again) and I believe that this is jealousy over Lucas' success. And also, his personal life seems to be falling apart (Empire Of Dreams again)....so I think he just wanted to be done with it. He did a quick and easy job on Jedi...hired all the people who he could control and just did it to be done with it.
And that attitude has carried over to the prequels.....he's doing these just to be done with the whole thing....and it shows in the story.
Bottom line....success killed Lucas. He got the fame, the glory, the money and he just let the quality go. It's happened to so many that it's really not that surprising either.