Empire Strikes Back was directed by Irvin Kershner, and written by George Lucas (story) Leigh Brackett and Lawrence Kasdan.
Return of the Jedi was directed by Richard Marquand, and written by Lucas and Kasdan.
If he wrote and directed Star Wars, why didn’t he do the same for the next two flicks?
P.S. I heard there was some ‘trouble’ with Marquand and Lucas assumed duties at some point during the filming, but that’s beside the point.
On that note, why didn’t he use the same formula with the prequels?
Why didn’t he direct them? Partly because he was setting up several companies at the time – LucasFilm, ILM, what would become the THX group, etc. And partly because directing Star Wars almost killed him – literally, he had a heart attack. I think there was a large fear component.
As to why he didn’t write them all on his own? Because he hates writing.
I think that he’s done everything on the three prequels to prove that he can. Probably got tired of people thinking of him as just a producer/business guy after all those years being, well, just a producer/business guy.
He had a severe, debilitating attack of common sense and awareness of his deficiencies?
Which he then managed to lose when he went to make Episodes I-III?
That’s exactly what happened. he thought he wasn’t very good at it, then realised he was so busy being an effects director for Empire Strikes Back, and really almost a complete director for Return of the Jedi (apparently Richard Marquand was pretty useless), and then he was pseudo-directing (when he was meant to just be Executive Producing) all the other projects he did since, that in the end he felt he really did have the skills necessary.
Skills, yes. Talent, no. He kind of messed up on that decision, but either he won’t admit it to himself, or he felt it was too late as he’d made the commitment and stuck by it.