No one here is likely to know the exact reason. Unless they know something broad about the Xbox store*
Since it's on PS3's store... there must be a reason but I don't think we'll know why exactly.
*I don't know anything about Xbox or the Xbox store... but I did give it a few googles and it seem Xbox360 doesn't like day1 digital for "full" games... no reason given.. just some randoms talking about how it doesn't happen. They went on to say most xbox360 titles come out a month later on digital. I don't know if it's true or not... If it is true, want a crazy theory 100% guessing? MS has some sort of deal with physical game stores or something...
I think it's written on a stone somewhere that all games must be digital day1 for PS4/Xbox1. I remember something about that at their launches.. maybe I dreamed it.
