It's kind of the opposite of how real nobles were. Diseases from being overweight were kind of a badge of honour, because it showed how much of a noble they were - in the same way having paler skin did (and sort of, still does).
So being chubby and fat was seen as a sign of luxurious wealth.
Granted this is a magical fictional world, but like so many, it's inspired by a European setting, so it just seems a bit odd that it strays in this regard.
Though I imagine even the ye olden Europeans couldn't glamorise being really obese.