Two aspects here. First, the reason for the trial is essentially PR&propaganda, the charges can be absolutely arbitrary but they would be made public, so it ma

Two aspects here. First, the reason for the trial is essentially PR&propaganda, the charges can be absolutely arbitrary but they would be made public, so it makes sense to choose charges that the elites want to advertise. Effecting political change by labeling the previous policy (along with its implementer) as treason and 'counter-revolutionary' is effective - it signals what they want to signal. On the other hand, advertising one of the elites as a rapist would not have a desired effect on the people's morale. Second, murder and rape were considered less important crimes than 'counter-revolutionary activity'. Slaughtering, torturing and raping people was frowned upon unless you had a good reason or these people weren't considered "proper people", but acting against the state apparatus is something that will be prosecuted with extreme prejudice and violence. And that's the message that was intended for the masses. Not rule of law, but obedience and following the official position. It's imperative that everyone understands that the law won't protect them if they act within the letter of some act but against the will of the state/party apparatus, so some arbitrariness within the trials and executions was intentionally designed, enacting punishments known to be random with the explicit goal of establishing terror (Starting with https://en.wikipedia.org/wiki/Red_Terror https://en.wikipedia.org/wiki/Red_Terror and followed up by Stalin). You can't instill proper fear in the population if they believe that simply being innocent is sufficient to be safe. There's a quote that's very old by that time but still relevant: "Do not look in the file of incriminating evidence to see whether or not the accused rose up against the Soviets with arms or words. Ask him instead to which class he belongs, what is his background, his education, his profession. These are the questions that will determine the fate of the accused. That is the meaning and essence of the Red Terror." The system really did not care that much about crimes against individuals, no matter how depraved; "crimes" of inappropriate political acts were more important. Some of the people who tortured others (who were later 'rehabilitated' by the state, admitted to be innocent) in late Stalinist KGB and gulags are still alive. They have not been tried or convicted or condemned, they're still receiving awards, honors and monuments in modern Russia. There has been no reconciliation as for most other totalitarian regimes.