The average journalist thinks they value the truth, accuracy and fairness. Observed behavior is very different to this flattering self portrait which is why they aren't trusted.
Actual behaviors of real journalists that create distrust which can't be blamed on advertisers or editors:
- Accepting large grants from billionaire foundations that are tied to pushing specific agendas and views. Example: look at how much money the Gates Foundation gives out in journalism grants tied to his personal agenda.
- Publishing stories that contain obvious "errors" (invariably convenient for their pre-existing agenda). Example: the NYT published a front page that consisted solely of the names of 1000 people who had supposedly died of COVID. It was meant to scare people and it took some rando on twitter about half an hour to notice that the 6th name on the list was of a person who had been murdered.
- Refusing to admit when they've misled people in the past, disinterest in publishing post mortems of their failures. Example: the lack of contrition over the Russiagate conspiracy theory.
- Point blank refusal to challenge certain types of sources because they think it's immoral to do so. Example: the BBC decided some years ago that climate change was "settled science" and that it was morally wrong to report on anything that might reduce faith in the "consensus". This is the opposite of the classical conception of journalism (challenging authority, digging up scandals, get both sides of the story etc).
- Relying heavily on sources that are widely known to be discredited. Example: Fauci stated early on in COVID that he lied about masks in official statements to the press, specifically to manipulate people's behavior. This did not stop the press using him as a trusted authoritative source. Another example: the way the press constantly cites academic "experts" whose papers are known to not replicate or which have major methodology problems.
There's way more.