Who pays to have their ads displayed by a chumbox? Probably smaller players but I can't imagine a reputable company to post ads in that toxic environment, it really does look bad.
Previous discussion:
https://themargins.substack.com/p/taboola-outbrain-and-the-c... (https://news.ycombinator.com/item?id=20409693)
https://www.nytimes.com/2019/10/04/business/media/online-adv... (https://news.ycombinator.com/item?id=21175145)
The answer is "sleazy bottomfeeders", if the Taboola ads I've seen are any indication. Supplements, worthless insurance, colon cleansers, and the like.