Most medium to large media companies do have their own sales staff for online advertising! The problem generally is that they can't sell enough local/direct-sol

Most medium to large media companies do have their own sales staff for online advertising! The problem generally is that they can't sell enough local/direct-sold ads at a high enough CPM to sell out their inventory. This is where they use something like AdSense, to fill in those gaps where they couldn't sell anything for a higher rate.