I feel like they did that as a red herring. What little we could see of them from the trailers made it look like they were going to be the primary antagonist force of the movie, whom the miners were all directly working for as slaves, with Sentinel as their unwilling puppet governor likewise forced to serve them. That impression hid the truth of Sentinel himself being the main villain while the Quints were instead looming in the background as a bigger threat than Sentinel but one less relevant to this chapter of the story, like how the Emperor loomed in the background of main-villain Darth Vader in The Empire Strikes Back.Hell, throw a large, scary, non-transforming Quintesson in that subline too. Why that was a Prime Changer is beyond me.