My guess is that fatter women are lower maintenance, so less stressful when you have enough stress already.
Other possibility is any such proclivity is a leftover from our stone age ancestors, when fat was associated with times of plenty and skinny with times of shortage, which would be times of stress to escape. Hence an attraction for anything associated with ample food supplies.
"I've got fudge, Hershey's Chocolate Kisses, we're talking Haagen-Dazs baby...what do you say?" - Andrew Dice Clay