Because that doesn't advance their agenda.
And that's what all the hullaballoo has been about from the beginning. Al Sharpton forced his way into this story looking to bolster his ratings. Jessee Jackson and the professional race baiters moved in looking to maintain their relevancy. Trayvon's mother trademarked his image looking to make some easy cash. Obama used this case looking to score some votes. The Justice Department sent down "community organizers" looking to keep their guy in office. The DA was all the time looking to score political points and improve her career. The police chief, warned by the example of the previous police chief who got fired because he wouldn't arrest Zimmerman, arrested Zimmerman looking to keep his job. Multiple newspapers, MSNBC, ABC, and the like doctored recordings and images and wrote damning op-eds convicting Zimmerman over and over again looking to get some ratings.
And no one was looking for justice, just their own agenda. And George Zimmerman is the one paying the price - paraphrasing from a post I left on my local newspaper this morning. It's always been agenda. The NAACP is now pushing theirs looking for more donations. If the stories about the Justice Department are true, well, they're looking to save themselves from embarrassment. I don't think it's going to end soon or well.