Similar to what happened earlier in the year where Lord and Miller were fired from the Han Solo 2018 film and replaced by Ron Howard, Disney has let go of Colin Trevorrow, who was set to direct Episode IX, and instead Force Awaken's director JJ Abrams is taking the director's seat once again. Like the Lord and Miller situation, Trevorrow was released due to "creative differences," but another big reason why it looks like he was let go is because this past summer Trevorrow released a drama film called "The Book of Henry" which was not only widely panned by critics (earning only a 22% on Rotten Tomatoes), but was also a bomb at the box office ($4.4 million earned compared to a relatively cheap $10 million budget, doesn't exactly look good to any studio execs).
Disney likely didn't want to take any chances letting Trevorrow continue to direct when right now it looks like his reputation as a director has been hurt by a film that reviewed badly and failed to make back even half of its budget, especially given Episode IX is meant to be the end of the current sequel trilogy.