> for smallish advertisers (this is not P&G, I understand) agencies can negotiate much better terms
It's more than that. As a small business managing your own ads you can get your account suspended without explanation and any way of recourse just by raising some flags. But being a WPP subsidiary you get assigned an account manager that guides your team trough the process, shows up with presentations, gives early access to tools and ad formats not (yet) available to the general public and makes sure your doubts get resolved before the ad goes live. If you get flagged, they call you to help fix things.
Keep in mind WPP spent $2B on Facebook in 2017, which is 5% of Fecebooks $40B revenue that year. Similar with Google, WPP brought in ~$5B out of $110B Alphabet's revenue.
It's more than that. As a small business managing your own ads you can get your account suspended without explanation and any way of recourse just by raising some flags. But being a WPP subsidiary you get assigned an account manager that guides your team trough the process, shows up with presentations, gives early access to tools and ad formats not (yet) available to the general public and makes sure your doubts get resolved before the ad goes live. If you get flagged, they call you to help fix things.
Keep in mind WPP spent $2B on Facebook in 2017, which is 5% of Fecebooks $40B revenue that year. Similar with Google, WPP brought in ~$5B out of $110B Alphabet's revenue.