Adding on to the question: Why did people like Lenin, Stalin, and other Russian revolutionaries get similarly mild punishment when there was no apparent barrier to just executing them?

The standard answer given to this question is that it was a result of the pro-Nazi leanings of the judges at the trial. It wasn't a jury trial in the way we think of them, but rather a trial presided over by a regular judge and several lay judges. The regular judge, a Bavarian jurist named Georg Neithardt, was especially lenient on Hitler, while the lay judges were more or less pro-Nazi in their leanings. Instead of being put on what we, today, might consider a rigorous trial, Hitler was mostly allowed to grandstand, arguing that while his actions might technically have been illegal, it was only in the technical sense and his motives had only included raising Germany back to its rightful place. It's similar to the way extreme right-wing political rhetoric often works - they are not acting against the state, per se, so much as acting to restore the state to the place it would be if the criminals who were really in charge could be removed. That is to say, it's not the extreme right-wingers who are the "real criminals" but rather those who are already in charge of the state apparatus, while the right-wingers are actually acting in the best interest of the state.

This question was asked one year ago and I think the top comment given then was quite good: https://www.reddit.com/r/AskHistorians/comments/26yca3/why_wasnt_hitler_executed_for_treason_after_his/

But Hitler got one of the most conservative and right-wing judges in Bavaria. Instead of trying Hitler as a traitor, he allowed the Hitler (who defended himself) to use the trial as a platform to spew his ideas for Germany. Hitler's trial became a sensation, and it catapulted Hitler into the center of Germany's right-wing politics.

I would also like to add that the support that would give Hitler the post as chancellor ten years later was not only built between 1923-1933, even though the nationalsocialists of course was good at propaganda and creating support for themselves, but by men much earlier. The idea of pan-germanism (all germans under one state) had spread rapidly in Germany during the 19th century and the nationalsocialists had much support to gather from the many followers of this idea.