Sauce for the goose?

The DPP is coming in for heavy criticism over "Operation Elveden" - this was an investigation into journalists (almost all from the Sun and the now-defunct News of the World) paying public officials for confidential information which was then used to publish "exclusives" in their papers.  Why the criticism?  Well of the 29 prosecutions brought against journalists, only one resulted in a conviction, so she is being accused of wasting a significant amount of public money pursuing journalists who, as they saw it, were merely "doing their job". But at the same time, 26 public officials have been convicted under essentially the same evidence for taking the money.  And I find it difficult to get my head round the idea that accepting money for confidential information is an offence, but offering that money is not.  Surely inciting someone to break the law is itself an offence?  Or are journalists somehow a special case?