Facebook, Google/YouTube, and Twitter to a lesser extent, command a large portion of the digital ad market due in no small part to the fact that they are also s

Facebook, Google/YouTube, and Twitter to a lesser extent, command a large portion of the digital ad market due in no small part to the fact that they are also some of the largest publishers. In other words, they make a ton of money selling ads on their own properties. Their publisher products (Adsense, DFA, Audience Network, Audience Platform) extend their reach to third parties certainly, but AFAIK each of them still make more money from their own inventory.