“Mostly because it is probably true.”
I think we’d be surprised how much of it is factual (or at least close to factual, with a cynical spin, of course). After I saw it for the 3rd or 4th time, I started reading up on Stalin, and some of the most bizarre stuff started to make sense.
For example, there’s the scene where they open Stalin’s skull once he’s kicked off. Well it turns out that Stalin had ordered the collection of the brains of prominent Russkies after their death so they could be studied. Whether it actually happened with Stalin himself or not I don’t know, but it is a plausible plot detail.
I did some reading as well, and the vast majority was true. There were some typical Hollywood plot devices like time dilation (in real life it took them about 6 months to get around to killing Beria), but the majority of it was quite factual.
CC