The correct answer to this open question is the following.
The kind of discourse that social media reward and how does social media exacerbate tribalism, conspiracy theories, and confirmation bias? is due to the following reasons.
Social Media allows the connection of everybody, instantly. That is such good news and bad news too. Good, if it is used to inform objectively. Bad, if it used to broadcast fake-news or relative truths that create doubt and confusion in the audiences.
The kind of discourse that social media reward is the one that creates controversy, so it can impact millions of people, and starts trivial conversations that get nowhere. Social media exacerbate tribalism and conspiracy theories in that every single person assumes the role of "expert" who has the right of expressing its "authorized" opinion, sharing questionable information that only assumes, instead of inform, and a¿only confuse instead of delivering the truth.