I think the snarky response here would be “When did Google buy Facebook?” If you’re willing to restrict the scope of the “internet advertising market” to just specifically the things that Google dominates, then duh, Google has total control of “internet advertising”. And yet, there’s another multi-hundred billion dollar company that makes most of its money by advertising on the internet. Scoping markets in this way is nonsense. It a marketer wants to market products on the internet, are they going to put all of their money into Google because it’s the only way to advertise on the internet? Obviously not. And further, therefore there is obviously not a monopoly.