I'm not saying it doesn't work because it does, usually more for the advertiser and not the publisher. Wanna know the secret why it doesn't work, get ready for it, here it comes... NO ONE CLICKS ON ADS. Ever go to one of those sites and see the thing covered in ads and pop ups. I can almost promise the first thing you do is try to minimize them, then get annoyed because they keep coming back and the just leave the site.
See all these fancy ads I have here. Not alot just a few. sift around the screen there and look you'll see them. Here's the second resaon why it doesn't work. You don't really get paid for people viewing the ads. well you do but it's not enough to buy a pack of gum, probally not even enough for a paper clip. I only make any thing once those ads are clicked on. Heres the thing like I said no one click on ads. So you (the publisher) basically make nothing but just from your readers seeing the ad it gets the advertisers name exposed to the world. See the problem yet?.