This isn't anything new.  Who knows how many companies went out of business when google changed their search algorithms, or when Amazon moved into other ventures besides selling books?

This will continuously be an issue as long as people still use others as a means of distribution.  The exact same thing could potentially happen here on Steemit, even if it is decentralized.  Steemit could always move to change the "trending" or "hot" page algorithms and people who have been able to make a good living that way would have to adapt.

I honestly don't think that Facebook did anything wrong here.  Don't like the way they do things? Find a different outlet.