According to research firm Pivotal, Facebook and Google accounted for 73% of all digital advertising in the US in 2017.

Add here Amazon and few other big guys and it'll be almost 95%.

Unilever has threatened to withdraw ads from platforms like Google and Facebook if they do not do enough to police extremist and illegal content. "We cannot have an environment where our consumers don't trust what they see online," said Unilever's chief marketing officer Keith Weed. He said it was in the interest of digital media firms to act before "advertisers stop advertising". Mr Weed said companies could not continue to support an online advertising industry where extremist material, fake news, child exploitation, political manipulation, racism and sexism were rife.

To translate it to normal language - owners of Unilever who re also owners of top advertising firm publically demand (as it is just play for public) to make (and improve later) censorship tools for all social media, as well for private external sites (Google will pull all advertisement if they won't like your content).