Journalists were always activists in some sense. You need to have a strong moral sense to uncover truths that power wants to keep under wraps, you need to have a strong inner motivation to seek out information that can get you or loved ones harassed or even harmed.
Trust has eroded because the business model for journalism has eroded, with a lack of money the news had to look into tapping other sources of income like pay-per-click ads, to increase that you need to have clickbait, ragebait, all kinds of manipulation to make someone choose to visit your news site instead of the 100s of others that popped up on the internet. With that you start losing trust.
Also I believe your view of journalism is very likely an American one, with your 24/7 "News" channels that are more a drama-generating machine than actual reporting, or investigative journalism.
There's still a lot of good journalism being done, and nowadays a lot outside of the usual institutions of news where investigations could be done before but got eroded because they got poorer.
Journalism necessarily requires some level of engagement and activism, I just don't think what you mean by "activist" is the actual meaning of the word but a catch-all umbrella for stuff you don't like. Would love to be proved wrong though.