That was a few years ago because Glee isn't up against NCIS. NCIS is on Tuesdays and Glee Thursdays. Raising Hope is on Fox Tuesday and in 18-49 NCIS double Raising Hope's rating.
Meanwhile on Thursday, Glee is soundly beaten by Person of Interest on CBS in the 18-49 demo by over 50%. Glee seems to only be able to beat PoI when PoI is in rerun while Glee is first run AND follows American Idol. Otherwise Glee has trouble getting into the top 25 shows in that demo. That affects ad buys as advertisers would only consider Glee under those circumstances. Otherwise they can advertise elsewhere and get more viewers, particularly on CBS.
Here is last week's 18-49 numbers
and they're dominated by CBS.
But Coke's demo is more than 18-49. Their demo is everyone with a heartbeat. This isn't Sony with the Playstation. And CBS is a ratings juggernaut...everyone wants to advertise on those shows. CBS needs Coke, Coke needs CBS.