Basically, because it serves him... and his politics.
An editorial which appeared in yesterday's Wall Street Journal asked this important question, pointing out how Eric Holder and Barack Obama use unrelenting manipulation of racial tensions for political purposes. It's worth a read:
The United States of America has a black President whose chief law enforcement officer, Attorney General Eric Holder, is also black. They have a lot of political power. So how are they using it? Well, one way is to assert to black audiences that voter ID laws are really attempts to disenfranchise black Americans. And liberals think Donald Trump's birther fantasies are offensive?
"In my travels across this country, I've heard a consistent drumbeat of concern from citizens, who—often for the first time in their lives—now have reason to believe that we are failing to live up to one of our nation's most noble ideals," Mr. Holder said Wednesday in a speech to the Council of Black Churches. Voter ID laws and white discrimination, he added, mean that "some of the achievements that defined the civil rights movement now hang in the balance."
That's right. The two most powerful men in America are black, two of the last three Secretaries of State were black, numerous corporate CEOs and other executives are black, and minorities of many races now win state-wide elections in states that belonged to the Confederacy, but the AG implies that Jim Crow is on the cusp of a comeback.
It's demeaning to have to dignify this argument with facts, but here goes.