There are loads of reasons, among them western propaganda, but also how so many of the more structured western communist groups either became fed central or just had the leadership taken out. Anarchism is harder to root out not just because the feds are light on it, but also because who are you supposed to assassinate to take them down?
A significant amount of it is also because the big authorities they directly experience and oppose suck. If you oppose the US for it's authoritarianism, why would you not oppose other places for authoritarianism?
Of the multitude of reasons, that’s one of the least in my book. It’s not about authority, it’s about how it’s wielded and against whom.
There’s nothing inherently wrong with authority. It’s about what systems and people it’s protecting. In the case of the US: it’s property and the robber baron class.
People grow to assume that authority where they live is authority everywhere. You grow up your whole life suspicious of American cops, you aren't likely to think cops are super cool, even if they're revolutionary and Cuban.
I would say that, under a strong implementation of democratic centralism, assassination is not a significant issue. Previous democratic centralist implementations have a history of being heavy on the centralism, light on the democratic, but if the party line really does come from the bottom up, the leader is only the most effective organizer. They do not need to be a visionary so much as a logistics nerd.