That absolutist power "off with his head just because I don't like his face", might have worked some 1000 years ago (although it might still be a perception problem).
But having (almost) read "Beria - My Father: Inside Stalin's Kremlin" ( https://www.amazon.com/Beria-Father-Inside-Stalins-Kremlin/dp/0715632051 ) it seems even the cruelest dictators need to walk a thin line of intrigues, deceit and shaky alliances.
Like, Stalin was afraid of Beria almost as much as Beria was afraid the former might get his head. But to get one's head, Stalin had to get the approval of the apparatus (they were more than willing to backstab someone, oftentimes not realizing it was Stalin who played them against each other). One advice by Beria to the guys who he tried to protect was "never execute an order which wasn't given in writing". Then, like now, it was very fashionable to claim ownership of successes but deny responsibility for failure, and nothing is more convenient than convincing or pressuring a sucker to do your dirty work for you.