That's because there was never a case for Russian Collusion to build. So Mueller is building a report to explain that it never happened & why people were deceived into believing that it did.
Building a report with people going to jail for belatedly telling the truth that the first story (collusion), wasn't true. Not people who got immunity to confirm the lies of other witnesses like in the Hillary emails case. 
If there was not collusion conspiracy, no one can confess to it. But people like Pdop, Roger Stone & Corsi can confess that the stories that created the impression of collusion were lies. Lies told for various reasons, by MI6 agents pretending to be Russian agents.
But with Russian Collusion, the primary crime was people telling false stories to create the illusion of collusion. So an MI6 agent pretending to be a Russian agent tells Pdop a false story about Russian dirt on Hillary. An Aussie diplomat tells a false story about Pdop & dirt.
So all of the crimes were telling false stories, which is why all of the crimes Mueller is finding are false stories. I believe it is clear that Mueller is investigating the conspiracy that arranged those meetings, planted those false stories, that leaked them to the press.
See Mueller's investigation & report is focused on how those narratives were created? What information was taken from NSA databases to concoct the? Who paid to have those reports written? Whose friends in Russia helped pretend to have dirt on Trump?
Who made all the smoke?
Who made all the smoke?
Who created all that smoke, from both the Republican establishment & the Democrats?
Who joined Trump's team as spies & to create more smoke?
That is what Mueller has been investigating, why he has put the screws to everyone. Why he is finding lies instead of collusion.
Who joined Trump's team as spies & to create more smoke?
That is what Mueller has been investigating, why he has put the screws to everyone. Why he is finding lies instead of collusion.
Because collusion was a lie. A very elaborate lie, that left a lot of fingerprints. Mueller is fooling people into thinking he is investigating collusion, because it tricks the media into not covering up the fingerprints of those who helped create & sell the lie.
More evidence that Mueller is not planning to prosecute anyone for Russian Collusion. He is planning to expose that it was a lie, some of it told by people willing to go to jail to confess that it was all a lie. Who would you believe is a liar? A convicted liar, prosecuted for it
But this gets to the crux of the matter. Mueller can report who those corruptible people who joined Trump's campaign were really working for. Like Manafort & Gates leading to the Swamp & Oleg Deripaska. Sent in to create smoke & sabotage the Trump campaign.
But this is where @AndrewCMcCarthy is wrong, it did happen to Democrats. I suspect Mueller's report is going to show that too. Bernie Sanders had Tad Devine, a Manafort associate, join his campaign as a Chief Strategist. Placing Bernie within 2 hops of Manafort's FISA warrant.
@AndrewCMcCarthy Bernie Sanders also had his family investigated by the FBI, including a Grand Jury targeting his wife's financial deals while President of a University. The Trump/Russia smoke generation, was also a tactic used against Democrats in the 2016 Primary & maybe before.
