Dune does not explain anyone's reasons for anything. It's just a bunch of archetypes archetyping. I'll save anyone who wants it, 6 hours:
"We do what we must, because we can"
"Aiiieeyyaaaa yaaaaaaa!"

Beautiful movie though. Absolutely stunning. What it lacks in character development, it makes up for completely and then more, in visual storytelling. I highly recommend the watch, but you'd probably take more from it just setting the audio to a language you don't speak and letting the settings and angles and lighting talk.