Could the ad networks scan the site instead and use the content on the pages to determine likely target audiences? You could still do ad networks, and target audience, based on the site that they are currently on.

The current version of adtech is pretty damaging to society as a whole and it's getting increasingly worse. Apparently nothing online or content related is able to generate enough revenue to keep itself afloat without ads. Manufactures of TVs and cars are collecting and selling data to increase profit, but are themselves buying ads, making it akin to a pyramid scheme. Maybe we need to start taking a look at the industries that are heavily depending on selling ad space to survive and question if they need to exist, or should be transformed into actual products.