I’ll play the role of armchair psychologist here and suggest that maybe being attracted to bigger women when stressed is something to do with reminding them of hugging their mothers when they were upset as small children...
... Which brings me neatly to the theories of Sigmund Freud...
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.
More likely that heavier women are more likely to survive when food is scarce (the original stress). It’s hard to get away from biology.