Their reasons are their own all that really matters now is that Rian Johnson brings us another great addition to the saga.

Steering the conversation actually towards TLJ:

are these Daisy’s eyes? I’m not sure exactly what this would have to do with Rey unless she turns to the Dark Side or something but I think it would be interesting as hell to delve into the rationales of our villains. Perhaps not to the point where we sympathize with them but to the point where we get where they’re coming from. There was a bit of this in Krennic and although briefly touched on it was one of my favorite parts of Rogue One.