In what sense? Legally they are, they act like one so I am not sure in practice what makes that distinct.

Perhaps you mean that user expectations makes them not "just a private company." In which case I see no reason why that doesn't also extend to pretty much any other much smaller platform in which users complain about moderation or opaque governance (reddit, twitter, linkedin, tumblr etc...). There are numerous examples of change.org petitions asking for kickstarter or some other platform to change how they do business.