Because that's what they do. Cover people's ass. Specifically liberals who screw up. They finally did a story on NASA's mission of manned exploration of Muslim outreach. And, as you'll see, they spend most of the story covering Whitehouse ass. That's right. CNN covers the news... mainly in the form of covering Obama's ass. (CYA).
They do it again here in the story of the Shirley Sherrod from the Dept of Agriculture. The CNN story is very long -- and more than half of it is allowing Sherrod and others to cover her ass. No conservative ever gets so much positive news page real estate.