As you say, the big platforms are FB, Google, and Bing. The only non intent driven advertiser on the big list is Facebook for a reason. According to this list,

As you say, the big platforms are FB, Google, and Bing. The only non intent driven advertiser on the big list is Facebook for a reason. According to this list, https://www.quantcast.com/top-sites https://www.quantcast.com/top-sites, Yahoo traffic is not insignificant compared to FB at all. With FB's targeting, Yahoo could be monetized soo much better. Most direct acquisition marketers I know would say that Facebook is the main scale player in non intent driven advertising, all because of its superior targeting.