I have two responses to this:
On one hand, I am glad I have a fetish that actually exists IRL. However I do find it a bit frustrating how rare attractive BBWs seem to be IRL, at least where I live. Hell, even when I visited the US recently, I didn't see very many. I think this perception probably stems from watching too much fat porn, but still. I consider myself lucky to have dated a few BBWs.
I also consider myself lucky that I'm not fixated on weight gain - don't get me wrong, I do find it hot, but I don't *need* it to get off. I think my romantic life would be even more frustrating if I did. (In other words, of course weight gain exists IRL, but I think actually finding a feedee would be nigh-impossible)
My second point is less specific to fat fetishism, but still tangentially related: I don't really understand how people can have fetishes for things that don't exist IRL. Furries are one example (as you said), but there are many others. Things like giantesses, vore, inflation, even things completely unrelated to fat, like hypnosis etc. Honestly, I find such things cringeworthy, but I'm trying not to judge. How frustrating would it be to only be able to get aroused by something that's completely impossible in the real world? Did people have these sorts of fixations before the invention of the internet? It baffles me.