Maybe I don't understand the complexity behind the ad-network curtain today, but direct ad sales worked fine pre-internet. Serve the ads from the same domain as your content and you can prevent ad blocking. Sounds like a win-win to me.
Yeah, I agree. The challenging is finding the relevant companies who wish to advertise and the ad 'sales' process. It's significantly more work than just plugging in an existing ad network who has a ready supply of ads, and it requires a slightly different skillset that's not necessarily a core competency. I'm going through the process right now of reaching out to relevant companies with an aligned privacy focused and it is a mixed bag of results.
Having said that, I think it is worth it in the long term because it makes you less reliant on other companies, but it is a tremendous amount of work upfront.