It's absolutely not as simple as a biography versus science fiction.
It seems Straight Outta Compton is fictional too:
Here's What's Missing From Straight Outta Compton: Me and the Other Women Dr. Dre Beat Up;
[Link: gawker.com]Really, could you even start to imagine that those guys would tell the entire truth about what thugs they were? Are?
Of course, I don't think the Academy checked out how accurate the story was. They just didn't vote for it. And maybe most of the academy members hate rap and hip-hop anyway, so why would they vote for a story about it? Here, finally, we connect the result with the bias of the members.