Argued to the extreme, there could be infinite variations of content that you could route users to, and the routing algorithm is so good that it effectively 'controls the content' by selecting which exact content to route to, even though technically speaking they are not controlling the content.
This kind of hairsplitting is basically the 'have cake, eat it too' situation.
It's just that companies like Facebook, Twitter etc don't want to attract negative PR attention by being the first to move. Once one of them does move it's far less risky to follow.
It is not unlike a mob. While it is comprised of autonomous individuals, there is a feedback loop of their own making that results in an emergent behavior. Translated into moonman talk: something something social contract, something... collective will.