the speedrun to the end happened because originally it was supposed to be a two part movie - the first draft is the proof - more or less like the Villeneuve movies ending with the Harkonnen takeover and then switching to Atreides comeback in the sequel. Dino was on board with that and then Universal who paid for it said "NOPE" so the story was remodeled into one movie long movie and thats how it went into production. And then the test screenings went badly and the movie got reedited into a two hour running time making it even less coherent.