In 2015, Facebook started driving more referral visitors to publishers than Google.
It didn't last long.
By July 2017 Google was back on top. Now, Google from providing a low of about 33% of traffic against Facebook's 42% in Feb 2017 moved to providing about 45% against Facebook's decline to about 20%.
Search Engine Optimisation is back. Facebook is declining.
Invest in SEO.
Having said that, it's really just a Facebook problem. Other social sites seem not to have declined. Pinterest is still good.