BECAUSE IT'S VERY DRY AND QUITE EXPANSIVE.
Now buckle in because that's the only light-hearted bit you're getting. Gibney's sprawling account of Russian ties to the 2016 US election is a massive achievement and rather meticulous - and like any piece of investigative journalism it doesn't really answer any questions or provide many simple truths. It's pleasingly intricate and despite being deeply American doesn't opt for many of the hyperbole that mires US documentary work.
In terms of the subject matter there's rather a lack of American investigative journalists - you've got a Yahoo! News journo but most of the US talking heads are sincere but biased big-hitters like former deputy director of the FBI or National Security Council member Celeste Wallander. This is a choice of course, and hearing from some of the central players in the narrative is quite compelling, although it means that you only get the merest tantalizing glimpse of the larger social context for a lot of what it all means beyond fairly high tier political figures, however odd they may be.
As other reviewers have hinted, as enormous as this documentary is, there is likely an even larger story at play here and these elements that Gibney has laboriously pieced together is only the view from the present. What revelations are to come are going to be all the more fascinating - and hopefully will be communicated in a slightly more succinct fashion.