I think this is it.
Despite all the emphasis in sex, gender, and racial diversity, there is actually almost no real diversity among the staff.
What they are typically, regardless of those other things, is from university educated, urban or sometimes suburban, middle class or upper middle class families. And their worldview and politics reflect that more than anything else.
A healthy media depends on people coming from really differernt perspectives which in this case would mean people who did not come through journalism studies and universities, people who are not all rural, and people from differernt kinds of economic backgrounds.
Which should be easy, because no one needs a degree to be a good journalist.