A lot of onlyfans is the social element. The smaller acconts tend to engage with their subscribers on personal/emotional levels. Big ones make a show of throwing open windows into their life and happening/personality. It's similar to streamers or "content creators" or "influencers" in some way that they are D or C list celebrities that let you into their life for a false sense of closeness. Also some of these people have a fetish in being simps or whatever. As weird as it sounds. To some also the exclusivity has an appeal. You are a subscriber, you show up on the radar in some maner, only you and a select group of others are in on it. Versus anyone being able to google big booba and it being a merely extractive relation of you taking the picture and being done with it.
Finally humans tend to make cults and objects of worship. You can see it all around you if you stretch things a bit and look at it from certain angles, why do so many people obsess over Lebron or Messi, why do they create these communities with these rituals and inside lingo and sacred things. Communities too. It's somewhat indicative of the irreligion and shattered inherited communal bonds a lot of people struggle with. Humans may or may not be somewhat predisposed to community and some sort of religion in Durkheimian terms(no need for supernatural or Deities). Or a king/leader to bow to/follow.
Certainly these people aren't retarded to be simply in on it for big booba if they can find big booba for free. There's more to it and there's digging to be done there.