Perhaps, since the director is involved in several continuations of franchises coming up, the answer is that James Cameron has simply hit his level of superhero fatigue.
I know my sister skipped both Wonder Woman and Black Panther because there have been so many superhero movies in recent years, and some have been disappointing.
Perhaps that will be Avatar 2 when it finally makes its debut on the big screen — doubtless that is what James Cameron is hoping, as the movie will need to make plenty of money to earn its budget back.
At this point, I’m just trying to get her to Deadpool 2; the point being that there are certainly people out there who have had their fill of superhero movies and are ready for some other trend to take their place.