"My hypothesis is that rightism is what happens when you’re optimizing for surviving an unsafe environment, leftism is what happens when you’re optimized for thriving in a safe environment."
https://slatestarcodex.com/2013/03/04/a-thrivesurvive-theory...
If you're trying to push as many people as possible to a "survive" mentality, I assume a divided and polarised community helps. Others are coming for your stuff! For your jobs, for your neighbourhood, for your status quo, etc. Make out that your opposition is some ultimate evil.
A more diverse political field and different voting system would likely help. Might stop single issues dominating the playing field? Bring back some nuance.
I think it's too simple to say "the media wants sensationalism" because we all collectively favour sensational content. It suits for-profit publishers, it suits politically active people, etc. But we're making it work for them. We can pretend we're above it, but if @dang let through all the Musk threads on HN, many here would turn full-time arguing in them.