With Star Wars: The Rise of Skywalker wrapping up a forty year saga, while also bringing back Emperor Palpatine and concluding the story of Rey and Kylo Ren, one could easily see there being two movies’ worth of material available. But two films wasn’t the way to go as the Sequel Trilogy was meant be just that: A trilogy
“George always said it was nine movies,” Rise co-writer Chris Terrio said in a recent interview with AwardsDaily. “That was the natural size of the saga, and so, other than a few initial discussions, we never really advanced that conversation.”
Source: IGN.com Star Wars: Why There Won’t Be a 10th Skywalker Saga Movie