That's only 1 of many reasons. Another big one being it's a lot more time-consuming and costly to run your own ad sales team, you always have to worry about fil

That's only 1 of many reasons. Another big one being it's a lot more time-consuming and costly to run your own ad sales team, you always have to worry about filling all ads in all countries, and the average CPMs you get may not be nearly as good as the ones without any headaches from big ad networks (well, headaches from the advertiser acquisition perspective).