From the start, Francis made it clear he preferred if they adapted Ballad of Songbirds and Snakes as one movie, but make it the longest Hunger Games film. He added, “I mean, not a lot of people mentioned [splitting it into two parts]. It was brought up, like, ‘You could do it because it’s a long book,’ and I said, ‘No way.’ So, I said, ‘No, you know what, I would rather do a long movie, and have it be one, full satisfying piece.”

Source: https://www.buzzfeed.com/noradominick/hunger-games-ballad-of-songbirds-snakes-facts