Google and Facebook don't just dominate online ads—they're pushing everyone else out, too

Advertising was once a huge but varied industry. Newspapers, TV, radio, magazines, billboards, and plenty of other media competed for their own piece of the pie.

The digital world could not be more different. Online ads are dominated by Google and Facebook—and they're only getting bigger. Google and Facebook are projected to take up 63.1 percent of U.S. digital ad spending in 2017—even more than had been initially expected, according to eMarketer.

That's not set to change anytime soon, with eMarketer predicting that the Google/Facebook duopoly will grab even more market share—a full 2/3 of the market by 2019.

This dominance is coming under serious scrutiny after recent revelations that Facebook's ad platform was used by Russia to target ads related to the 2016 U.S. election, as well as the discovery that Google and Facebook allowed for the use of anti-Semitic and racist terms in ad targeting.

There's plenty of also-rans, including Microsoft, Amazon, Verizon (and its Oath properties that include AOL and Yahoo), Twitter, and Snapchat. They offer advertisers some upside, but don't have the targeting that Google and Facebook offer.

“Advertisers are increasingly demanding more granularity in targeting capabilities to reach consumers,” said eMarketer’s senior director of forecasting, Monica Peart, in a press release.  “Google and Facebook have positioned themselves at the front of this demand curve by being the ad publishers with some of the best-in-class targeting abilities in the digital ad market. With Facebook being able to provide targeting based upon consumer interests and Google capitalizing on where those consumers have been through searches, both companies ensure their lead among digital ad publishers.”

The biggest loser, according to eMarkter, will be Twitter. The microblogging platform is projected to endure a revenue decline of $1.21 billion.