You mean he's not interested in telling us serfs what to do, what to buy, and how to live? He is avoiding his extremely important role for the most intelligent of us all, actors? The nerve of that man!
I think in this movie's case, Lucas stopped by because he's been friends with Ron Howard for 45 years, at least. I wouldn't be surprised if any SW set would welcome his visit just because he's the creator of it all. I would hope that they would be asking him questions like "Would Luke do something like this?" you know, the stuff Rian Johnson didn't ask...