So again, what was the motivation? Was Lucas jealous Kershner got so much credit for ESB and he wanted to stick his own contribution into the climax?
Nah, whatever it was, I don’t think it was that. If he was so crazed about credits he would have taken a screenplay credit for ESB. But he instead removed his credit and gave it to just Leigh Brackett (as an honor and tribute, although her screenplay was basically not used at all) and and to as a special thanks for coming aboard at quick notice to help him polish it up a bit. Although it seems, for some reason these days, mayeb all the Lucas haters flooding the internet with seething hate, to be mostly forgotten, Lucas actually wrote the bulk of the basic screenplay for ESB and even good chunks of the key, beloved dialogue was from his own original drafts.