I disagree, Greg. It's driven by a political process in which ardent loyalists select party candidates who then seek to implement the desires of their supporters when in office. Any attempt to work across the aisle is seen as weakness and, come the next election, you can guarantee there will be a competitor who's further to the right or left (depending on the party) of the incumbent, so the ardent loyalists can push to even more extreme representation.
The above problem is exacerbated by the information age which gives everyone a mouthpiece, and in particular it gives politicians a megaphone for their parochial perspectives...and they use them to keep the ardent loyalists on-side. It doesn't help when "fake news" is used as a mantra to disbelieve anything in the media...which pours fuel on the fire noted above.
I'm not saying the media is innocent but it's not all their fault. Some of it is structural and baked into the established processes, and some of it is just a lack of common decency in modern society. As a people, we've forgotten how to disagree without being disagreeable. .
I'll shut up now because I've already jumped too deeply into political issues.