Media organizations pay a fee. I believe they calculate an equivalent to a commercial airline ticket, which of course doesn't match the government's unique costs. This way the media can ask tough questions and aren't turning against their "hosts" in a way that could create a conflict of interest.

When I briefly worked as a reporter, I was instructed not to eat or drink at press conferences to maintain my impartiality. I know from sitting in the press box in stadiums that the major sports reporters did not feel similarly constrained!