I mean look at the extremely popular K-pop bands, fans get insanely invested into these groups, following them, bringing glowsticks to show support, etc. Or the entire Japanese idol movement for that matter.
Or think about how people stand in line for hours just to get the signature of somebody at a convention.
I think this is just the way a lot of people are wired. I don't know if it's bad or a good thing, it's just something I've noticed.
I do remember a study that people often think label their more popular friends as their "best" friends, but if you go ask THOSE friends, they label THEIR even more popular friends as their "BEST" friends. It's often asymmetrical.
Though tbh going too far down these rabbitholes usually isn't healthy/productive imo.
I still think there are multiple differences.
One is how OnlyFans has successfully turned everyday people into this source of para-social fixation for a multitude of small communities and somehow massified the issue.
The other and the main one for me is that in both the star system or the K-pop industry the system is a mean to an end - selling movie tickets or albums - while OnlyFans genuinely sells the illusion of closeness.
because OF models cannot realistically produce anything of that high production value to sell. They can take pictures, get videos shot, etc. And in any case, the closeness you speak also applies to the celebrity in mainstream industry.