“In the brand advertiser world CPMs have been the preferred measurement (people aren’t going to click an ad for Coke; instead its purpose is to influence you). For the past several years big advertisers on FB have actually been directing massive amounts of paid media to acquire fans. They quite literally bought likes.
Why? Early on FB made the case to brands that they must have fans… together with the ad agencies they convinced the Cokes of the world to spend money to be competitive (hey Pepsi is here too). Then, FB promised, something miraculous would happen. Your friends would see in their news feed you liked Coke!”