I’m skeptical that ads themselves actually have a return on investment. There are so many, they are almost entirely ignored. Of course the advertising companies have done a good job convincing people to buy ads. But do they work well enough to justify the cost?
Ads don’t make enough. I play a solitaire game that pays out money for sitting through the ads. Those ads are highly targeted and very likely to drive traffic to those other apps that say they will also pay you to play solitaire or even Candy Crush! I still only get maybe $.10 per game and sit through around 3 ads. I accidentally click ads a lot, too.
What else are web companies going to do for revenue, though? It doesn’t really cost them anything to host ads.