There may not be that much time between getting digital effects completed in post-production, and the film’s release, making the window for a trailer a small one.
The movie is only filming now and plans to hit screens in December, which is a remarkably fast turn around for a film of its size.
We’ll likely have to wait and see, at least until the first trailer, to get an idea of how Jumanji 3, which probably won’t be called that, will differentiate itself from the previous film.