That might be because "the news" isn't some abstract thing that has no effect on people's lives, so people want to talk to people about the news and politics.
Not saying you're wrong, but I don't know, I was perfectly happy chatting with friends on AIM messenger a decade ago. Myspace was also super spammy, but never became a (literal) news feed. I don't mind stupid pro/anti-Trump memes or whatnot, but giving news distribution companies (from Breitbart to the Economist) a platform on your social network seems like an anti-pattern.
I'd much rather see a news article someone thought was trenchant or interesting than a meme image that serves no purpose but to try and rile people up. Which one is a better basis for conversation?
Let me rephrase: I think it's perfectly fine to share news articles and talk about them, etc. But the distribution of news has become fundamental to FB and Snapchat (and to a lesser extent Twitter and IG) -- see FB's trending stories, or Snapchat's "Discover" tab. It's not at all like "oh Bob thought this Fox News article was interesting" -- although to be honest, I would actively discourage that, too.
I get a lot of news in my feed, but I willingly subscribed to multiple news sources and regularly comment on articles, so I can't comment on the idea of news being foist upon me.