They embed their ads on news sites, style them to look like legitimate articles, and prey on the vulnerable. Same methodology as the "your Social Security number has been suspended" scam calls.
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.