I don't think it's even that rare, it's just that it's a process for most people, not something that happens overnight. Which includes people who consider themselves marxist, communist, etc.; declaring yourself to be one doesn't immediately get rid of all pre-existing bougie schools of thought from your mind. I always think of Stalin talking about the USSR having self-crit. Or Mao's stuff like Oppose Book Worship.

If we understand ourselves as existing in many possible stages, with a process to transition from one to another, I think it's easier to see why it's both feasible to educate someone away from liberalism to communism and is also likely going to take time to get there.