In-depth interviews, early story tip-offs, and 'approved' leaks with accurate content aren't just a way to distribute information and build connections with reporters, they're a way to cultivate dependence. If 95% of unverified content is accurate, a reporter who can't get pithy 'official' quotes or advance warning on stories will consistently produce worse output than those who can.
It seems like a few particularly famous publications can push back because they're too big to shut out, though their individual reporters often still fold. (e.g. the NYT on Iraqi WMDs.) And there's a bit of room for dedicated 'dissenting' sources like The Intercept and CounterSpin, because they can curate a reputation as leak recipients and then fill out the rest of their schedule with media analysis instead of breaking news. But overall, first-line sources seem to be very effectively trapped by this pattern.
This is an important part of Herman/Chomsky's "Propaganda Model" of media.
It's actually worse, the power dynamics are completely lopsided: He/she can't disgruntle his governmental sources or else there's the very real possibility of being cut out of the loop/any access at all in the future.
Which isn't a great prospect for any journalist because you can't get any "scoops" when your competitors have privileged access to information.