Part of the problem is that Google and Facebook actually can know the audience better than the content creator. A content creator only knows that the reader is interested in, say, cooking. Facebook and Google know most everything the reader is interested in, and what sort of ads the reader actually interacts with. They can use all of that information to maximize the chance the reader will click on an ad.
The problem now is that because of how effective Google' and Facebook's ads are, a single click on an ad is basically worthless. Someone who's trying to sell a product isn't going to pay 100 times as much per click to use a smaller ad network, they're going to go with whoever can give them the most impact.