One way to think of it is a sort of multiplayer iterated prisoner's dilemma. If players generally cooperate, cooperating is the best strategy. If players generally defect, defecting is the best strategy. Over time you can get a death spiral (loss of social capital) where people defect more, which leads to more defections. You can also get selection effects where people who enjoy conflict stay, and people who dislike conflict leave.

The medium is the message. Certain specific features, such as the retweet-with-comment feature, incentivize starting fights. Older platforms didn't feature likes/retweets as prominently. Newer platforms are constantly giving you numerical scores, which leads to competitive socialization and status-seeking. Some people are into that sort of thing. And to be fair, clout is objectively valuable in certain ways.