Yes, that's a big part of it. That is in turn due to the differing approaches to the press in public and private sectors, which creates a self-reinforcing feedback loop.

Lack of trust in media is split strongly along partisan lines, at least in the USA. This is IMHO a result of the heavily reliance of the media on public sector / government / university / NGO employees as a source of quotes. Journalists like to present themselves as neutral voices but want their stories to sound informed, so almost every story must come with a quote from someone. Public sector orgs rarely punish people for speaking to journalists and often actively encourage it, as long as they promote the organization's goals and ideologies. Even when theoretically forbidden e.g. intelligence, military, what you see is a massive culture of leaks and off-the-record briefings that's tolerated and encouraged from the top. Universities meanwhile are pretty much quote factories for the press, with the result that in the media "expertise" is now synonymous with academia - journalists love the fact that academics are perceived as independent from their host institutions, can turn up on the phone or in a studio at the drop of a hat and there's an unlimited number of them to pick from.

By contrast in the private sector it's standard for communication with journalists of any form to be forbidden and penalized with the sack, regardless of the message being given. Employees are not perceived as independent of their institution, even when talking off the record or as an individual. It may not even be easy to find the right person to talk to.

This leads to a self-reinforcing problem in which journalists get repeatedly exposed to the ways of thinking found in the largest public sector organizations that have a well funded press operation, without getting any balance from other areas of society, making them sympathetic to those ways, which in turn discourages other kinds of people from talking to them because they correctly perceive the journalists as biased. The journalists shift ever further towards the views of the people who talk to them until they basically become arms of the state. As time passes this feedback loop has become so extreme that the media aren't content to merely repeat whatever public sector workers tell them, but actively persecute anyone who tells them anything in disagreement. The bias becomes ever more visible and trust collapses.

There doesn't seem to be any easy way to break this feedback loop. You can't tackle it from the supply or demand side. Trying to restrict who can talk to the press is probably hard or impossible, especially in the USA with the First Amendment. Trying to increase the supply of people outside the public sector willing to talk to journalists, also hard. The most obvious way forward is to support and encourage a different style of journalism that doesn't try to present a fake view-from-above, in which bias is injected via quotes from hand-picked pseudo-experts, but rather a more analytical and data oriented form of news in which the only allowed quotes are things people said to other people, in public. This is the style of journalism found on Substack.