The media does light fact-checking, and it's exactly that fact-checking that allows institutions to set an agenda. If a reporter sees a press release about a new study in, say, the field of cancer, and they try to fact-check it, they're likely to go and talk to the American Cancer Society. Which, as it turns out, has a point of view about cancer that it promotes.
What the hell else is the journalist going to do? They Just Can't read up all the relevant literature -- that's a full time job, and they already have jobs.
Interview some random scientist whose name they pulled out of a hat? That's not likely to help.