Advertisers will always pay more to Facebook and Google because they can target the right audience.
The click fraud on FB and Google is out of control, and most established news sites/publishers are desperate for revenue due to the insane growth of ad-blocker usage:
https://www.statista.com/statistics/804008/ad-blocking-reach-usage-us/
Within the next five years, most content producers won't be able to survive due to the high usage of ad-blocking software, and they will have no choice but to to turn to platforms like Brave.
And let's not even get into all the users FB is loosing with all their scandals. The future for Steemit/Brave looks very bright as far as I'm concerned.