There are all kinds of reasons why someone would be attracted to a "fat" person. Perhaps they have a social view that an obese partner means that they're a good provider. That they're not starving.
Perhaps they just find larger women attractive. Maybe they feel fat women are better in bed? Or perhaps they like food, and like to date people who like food as much as they do? How about they secretly have a fetish for it, or a fetish for feeding people, or...
Is there something about being obese that makes you unlovable here? Seriously, there's only so much to be gained from physical attraction. Once I was sleeping with a rather attractive woman, probably one of the most attractive I've ever slept with, when she uttered a phrase that could be commonly overheard in a trailer park. Instant boner-killer. Seriously, I got up, grabbed my crap and left mid-hump. Never talked to her ever again.
People have all kinds of standards and things they find attractive. I know a man who doesn't care how large a woman is, but he does care how large her breasts are. To him the larger the better.
Me? I'm more of an ass man.
"Well, then," the Cat went on, "you see a dog growls when it's angry, and wags its tail when it's pleased. Now I growl when I'm pleased, and wag my tail when I'm angry. Therefore I'm mad."