OK hear me out on this one because it may take some thinking hardly to understand but it makes perfect sense to me (and you) once you see what I'm talking about.
So its no hidden fact that most Western cultures view a slender body as more attractive than one that is chubby or even fat. Yes some cultures (ie Latin or black cultures) may view certain parts of the female anatomy as more desirable (ie fuller hips or asses) but the majority of Western cultures see women who aren't "skinny" as unattractive because they are "fat". World of Warcraft is a game that primarily has been developed in a Western culture company even though the game is a globally played game reaching many different cultures. More specifically World of Warcraft is a game developed by Americans that gets a worldwide release to players but is in the end developed by an American company. No one can argue that the American culture is all about fat shaming anyone who doesn't fit into the "fit" category.
That being said, let's take a look at some interesting facts about the game. Jaina Proudmoore, Katherine Proudmoore, Daelin Proudmoore, Tandred Proudmoore, and Derek Proudmoore are all Kul Tiran not Stormwind/Lordaeron humans. Not one of them use the Kul Tiran models at all. Jaina can be excused as she has been in the game since vanilla and there were no different body model types for Kul Tiran vs Stormwind/Lordaeron humans. The rest didn't arrive in the actual game (not speaking lore but in the game itself) until BFA when the Kul Tiran had already been established. Yes I could understand a possible need or desire to have the men appear to be more fit like the Stormwind/Lordaeron human men instead of the chubby Kul Tiran men but why not have Katherine at least have the body style of a female Kul Tiran. I'm not saying they needed to go all chubby like Priscilla Ashvane since she has her own unique character model which oddly enough is chubbier than a female Kul Tiran while the leaders and offspring of the leaders of the Kul Tiran are all more slender built.
So do you think that the Proudmoore family who are Kul Tiran don't use the Kul Tiran character models because of a fat bias that the developers at Blizzard have given they have Western beliefs because of them being Americans?