This might be a stupid question, but is it possible to monetise a website successfully using entirely "dumb" adverts with no ad networks involved? I mean ads which are simply an image inside an tag. Presumably this is how everyone was doing it before the ad networks existed? (I was around in the 90s but never really thought about it.) I guess it would take a lot of extra work and expense to approach potential adverti…
It is probably very effective if you have an audience with well targeted interests. For example a site about espresso coffee may partner with a shop that sells high end espresso machines and specialty coffee.
However, it is much harder if a website has a broader audience. A news network probably has no clue about what visitors want to spend their money on, so either they use an ad network that does the targeting for them, or they are limited to less beneficial generic partnerships.