To suggest there hasn't been a cultural shift is insane, imo.
I wouldn't argue that both sides have gotten more extreme, rather the political spectrum curve has flattened. There is much less rational discourse in general.
Reddit is a great example. Even 10 years ago you could have mostly rational discussions. Now its no better than Facebook. I saw a post today about people being upset the government is giving OpenAI half a trillion dollars. They didn't even realize it wasn't government money. They didn't want to be corrected.
the internet has a lot more people on it, it is much less self-selecting than in the past. even this website is a lot less self-selecting than in the past