I mean, on the individual level things are chaotic and complex enough that you can't always point to a specific person and say "this is why they believe what they believe that". But the predominant reasons I see with people is that they have enough awareness and interactions with the negative outcomes of the status-quo that they do not buy into the propaganda, by some reason like rebelliousness or curiosity read theory and get a better paradigm to understand the world, or they actually have some proximity to struggle explained in a socialist/leftist lens.