The sequel to Wonder Woman was planned for a December 2019 release originally, but when Star Wars: Episode IX was pushed back from its May release into December, Wonder Woman 2 moved itself up on the schedule as to avoid competition.
Jumanji isn’t going to go looking for an empty weekend, they’re stepping up and looking for a fight.
While Star Wars: The Last Jedi has certainly done just fine at the box office, Lucasfilm may want to take notice of this move because it’s a clear indication that at least one studio isn’t afraid of the franchise.
In the past, Disney has had their pick of the release calendar because frequently, once they picked a date, everybody else got out of the way.