Why didn't CNN fire Glenn Beck years ago?

We kept pointing out what a colossal ratings failure the right-wing talker was at CNN Headlines News. And here's the latest proof: Ever since Beck left for Fox News, CNNHN had been getting better ratings in Beck's old slot with a show hosted by a relative unknown, Jane Velez-Mitchell:

From the Huffington Post [emphasis added]

In its third full month on the air, “Issues with Jane Velez-Mitchell” posted HLN's largest 7PM audience since it launched its primetime block in February 2005. For January 2009, “Issues” averaged 531,000 total viewers and 221,000 Adults 25-54, a 50% increase in total viewers and a 46% increase in the demo over Beck's January 2008 ratings. Velez-Mitchell's January ratings also represent an 8% increase in total viewers and a 19% increase in the demo over Beck's last (and best) month on HLN.