That's not exactly true, to pick some examples Bernie quitting the race in 2020 used his connections with biden and got a lot of things into a unity party platform, and I've seen it argued that AOC and the green new deal pushed the overton window for the infrastructure recovery act, and while it definitely wasn't everything they hoped for, it did include elements, including a massive investment in clean energy.
https://www.usnews.com/news/elections/articles/2020-07-08/bi...
https://www.thenation.com/article/environment/thank-green-ne...
The Dems cooperate more, so the media highlights their occasional disagreements.