The Bolshevilks violently seized power.
For the Left in the West it was just handed to them. That’s the problem.
The Left started in the Universities which went out of their way to hire leftists and socialists and communists to demonstrate that they were “open minded” and believed in the “marketplace of ideas”.
If you want to conserve your institutions, you have to police the culture and agendas of institutions. But that thinking goes against Enlightenment Ideas.
Which is why anything based on Enlightenment ideas were bound to fail by internal subversion.
The Russian Revolution didn't happen overnight. The Bolsheviks had been getting their ducks in a row for years before 1917, infiltrating the institutions in Russia, waiting for the right opportunity to strike.