A Princeton study from earlier this year found that mainstream news websites use more third-party ad tech vendors than any other type of website: sports, shopping, adult, etc. Ad tech can slow down publisher sites if there are too many cookies dropped on a page, or if they're using certain techniques to capture data.
Going in-house: As a result, some mainstream news publishers are trying to reduce clutter by building their own proprietary ad tech to replace third-party vendors. Bloomberg and The Washington Post have have both been able to reduce page load times significantly by bringing ad tech in-house over the past few months.
News publishers and advertisers are both economically incentivized at this point to cut out the "middle men" in the digital advertising supply chain. Procter & Gamble Chief Brand officer Marc Pritchard told Axios last week he thinks only 40% of ad dollars make it to publishers after ads are done going through ad tech middle men.