It's a matter of scale in relation to your audience and data. Your local news site with users in the tens of thousands, is unlikely to have the capital to inves

It's a matter of scale in relation to your audience and data. Your local news site with users in the tens of thousands, is unlikely to have the capital to invest in geographic and demographic tracking necessary to provide a robust ads business. Easier to plug into a number of providers who already have that data about their visitors. These sites have to do that to remain competitive.