In other cultures, beauty is still the chubby/plump/whatever, instead of the american skinny.
In our culture, fat implies things like lazy, undisciplined, and apathetic. No one wants to be with someone like this.
In others, it shows wealth and excess.

You want to have wealth and excess. Look at the peacock. He attracts a mate by using extra energy to hold up the biggest, heaviest tail. By showing off the big tail, he is saying "I'm tough and kill shit, also I have extra food. Sleep with me." This is similar to rappers throwing away money in music videos or you buying an expensive car/house or just paying for dinner.