they were both taken out by the MIC of both nations because they were on the road to complete detente between the US and the USSR which would badly hurt their bottom dollar
the final straw was spoken about in Khrushchevs memoirs, which he had to record secretly and have smuggled out of the Soviet Union, where like a week before kennedys assassination they had a verbal agreement to turn the Apollo program into a joint US-Soviet program
the CIA and KGB caught wind of it and said enough was enough, the KGB hated Khrushchev as did the CIA with Kennedy, so they agreed to help each other out to get rid of the people standing in their way
not only that, but an agreement to share their UFO findings. we have the memo he sent to the CIA to have their files ready for the handover.
its really strange how JFK researchers just completely blindspot the Khrushchev connection desu, it never get brought up but its literally staring everyone in the face that theyre connected