Journalism can be sycophantic. Those who say too much of the wrong thing, can find themselves on the outside.
As a result, information perceived as being of greater 'risk' to the organization will no longer flow into the public domain.
The safest way to deliver this information, without repercussion, is via anonymity.
Anonymity is not the devil, but it can be, and it relies on trust. A great example of good reporting via anonymity was the Guardian's secret footballer series: https://www.theguardian.com/football/series/the-se...
One further point, a reporter/journalist, no matter what their qualifications or perceived level of integrity, is not a source.