as others have said, it's mostly presentation. the line between 'it's a fetish' and 'it's a type' really comes down to how you act for something like this. most people like when they're your type, relatively few like being your fetish. the difference is that being someone's type means you have a better chance at winning them over with your other qualities, but being someone's fetish means your other qualities are much less important.
think about it this way: imagine you have persistent acne. it's probably something you're insecure about. if an attractive woman says she thinks acne is cute, you might take that as a win, because hey, you might be able to score. but if she talks about it at length, maybe even says she wants to make sure you don't practice skincare, that you should eat an oilier diet to promote acne, you'd get creeped out. if it's an insecurity, you like a little compliment because it makes the insecurity seem like less of a burden, but the more emphasis someone adds, the more it feels as though your acne is the only thing that matters. that's not great even if you also have an acne fetish, and if you don't it's crushing.
this is basically true of all dating tbh. if you're looking for a relationship, you probably want to at least feel as if you're winning on your personality. even if they're totally conventionally attractive, most people will want to feel as if they're also a catch beneath the looks. for fat people, they aren't conventionally attractive, so they REALLY want to feel like they're valuable beyond appearance.