Few commercial directors are willing to dedicate themselves to causes such as SS, but would it be wrong to say that he looks an awful lot at the evils of the past (The Color Purple, Schindler's List, Amistad, and Saving Private Ryan--all great movies)? If he's going to do that, why not focus on the horrors of the here and now? As one of the most--if not the most--successful American directors, he could be making commentaries on the time that we live in (as well as reminding us of the past and what might be in the future).
It's a twofer: Spielberg gets to attack two of his favorite targets. What's not to like? Prediction: Box office disaster. Private bet?