They didn't choose activism because they are lazy or ideologues (although the industry may increasingly populated by lazy ideologues). The journalism industry chose activism because it sells better than objective journalism.
I could start an online paper about my local town and write purely objective stories. "Town council meeting today went as expected, complicated issue without clear solution continued unsolved". That probably won't get very many readers though. For one thing, relatively few people live in my town so few people will care. For another, the internet has conditioned people to get news for free, so the only way to monetize results in getting very little money (e.g. ads) from each reader, and, as just established, we'll have few readers because the town is small.
The revealed preference of news readers is to look at outrageous stuff and polemics. Get involved in a culture war about who did what why and what it means - that could attract millions of readers who you can slightly monetize to earn enough to get by. Do real journalism and few people will read it and they won't pay you won't for it... So...
I'm not saying this in a judgmental way. I don't pay for news either. I read what comes up on twitter, hackernews, linked to by friends, etc. I have an ad-blocker and I skip whatever content has a paywall that I can't bypass. I realize I'm part of the problem, but in a "tragedy of the commons" way. That is, the world would be better if everyone paid for and paid attention to primarily local and "hard-hitting" fair journalism, but there would be zero perceptible positive change if I switched to that model and perceptible negative costs for me for doing so.