* The media wants sensationalism, because sensationalism gets them peoples' attentions and thus money. There is nothing more sensational than riling up and pleading to peoples' emotions.
* The political powers that be want to keep the people divided. A divided people is easier to control and manipulate, whether it's smear campaigns during elections or undermining the safety mechanisms of our governmental institutions or straight up cancel culture.
How do we solve all this? Beats me, I'm in my mid 30s now and already tired of all this bullshit. I'll spend the rest of my days by myself in the countryside just enjoying the simplicities of life while y'all go and club each other silly.
Ranked voting would solve this issue. I have never read any critique of it that I found convincing. It exists at state and municipal levels. But until the big states switch it won't change the problem. If swing states adopted it, along with proportional allocation of electoral votes (a couple states do this now) it would definitely change strategies for the better.
The effect is that you can't be the most extreme version of your party and ignore moderates in the hope there are more people that hate the other corrupt extremist, because the moderate candidates will get ranked higher than you by both sides of the artificial duopoly.
In that world, the sensational nature of the media works to uncover sneaky extremists so you can rank all the boring candidates higher, or least higher than the extremist you don't secretly agree with. Either way the boring candidates win.
Someone once wrote that the best kings produce the fewest pages in history books.