Just a guess, but i wonder if those are the big agencies (which bring tons of clients).
The big ones are WPP, Publicis, omnicom…and then IPG, Others are regional like Dentsu in Japan.
TTD purposely pushes an agency-first mantra which keeps agencies loyal.
From 10Q:
“We had approximately 657 clients, consisting primarily of advertising agencies, as of December 31, 2017. Many of these agencies are owned by
holding companies, where decision making is decentralized such that purchasing decisions are made, and relationships with advertisers, are located, at the
agency, local branch or division level. If all of our individual client contractual relationships were aggregated at the holding company level, Omnicom
Group Inc., WPP plc and Publicis Groupe would each represent more than 10% of our gross billings for 2017.”
A good way to think about this is how ANET/Arista was reliant on Cloud Titans. That is what Agencies are to TTD.
Dreamer