Was it because he simply set too high a bar for himself with Titanic?
https://www.quora.com/Why-has-James-Cameron-given-up-a-huge-chunk-of-his-career-to-create-the-Avatar-sequels/answer/Rex-Mutero-1
According to what he said in the Behind-the-Scenes feature for "Avatar," it took that long to develop the movie technology he needed to make his film possible, and they simply didn't have it back in 1996-98. He wanted to make it immediately after "Titanic," but again, the special-effects technology simply didn't exist just yet. While people were using blue/greenscreen technology at the time, it now appears very crude compared to what he did later with the Na'vi and Pandora.
shareI haven't seen Avatar but the special effects don't look that impressive. I mean they seem to be in the same ballpark as Toy Story which came out years earlier.
shareFYI the special effects were an absolute knockout when "Avatar" was first released. It was one of the first films to make really amazing use of 3D, and it went 1000x further than any other film, and created an entire planet out of photo-real big-screen 3D animation. It was amazing to watch! Not so amazing that you didn't realize the hero was a dolt, but definitely worth $15 and two hours of your life.
It's just not the same on the small screen.
Yeah, but you'll remember, it wasn't until 1999 that "Star Wars Episode I" featured the very first, fully CGI character in a movie. Cameron's people took that to a whole different level with Avatar, in where not only did we have realistic-looking, fully-CGI people, but they were a completely different size and height compared to the human actors. They had to film every scene in at least three stages, and post-production (particularly with the Na'vi scenes) had to be worked on in three more stages.
I saw BTS photos and videos where the actors (when playing Na'vi or Avatars) had to wear these suits with the names of their characters on the chest, and they all had caps on with plastic Na'vi ears and colorful yarn to imitate hair movement. They also had mannequins that were the actual size of the Na'vi to act as stand-ins for some scenes, depending on what was going on. Truth be told, the most complicated part of a CGI-heavy film like that is the post-production, because the programmers, technicians, and editors all have to work together to make it look as good as possible, which is way harder than it looks. They've done such a good job, there are some parts that are CGI, but you would never know it unless they did a comparison shot between the set, and the finished scene!
You really should watch the movie, the visuals are far superior to "Toy Story."