I actually have the answer for you. See, industrial clothing has to deal with several industrial and management processes that hurt their ability to provide high quality, highly customizable clothes. They are forced to operate under a limited set of body shape models. For males, the most common is the inverted pyramid: broad shoulders, thick arms, thin waist, thin legs. For females, there are more shapes: apple-shaped, pear-shaped, guitar-shaped, hourglass-shaped, etc.  Now, fatties are amorphous: they have absolutely no shape at all. It's impossible to predict where fat will settle in a body. So, it doesn't matter how large the clothes are, they're still unflattering because they've been designed to highlight body parts most fatties would like to hide. That's what she's complaining about: it's not that stores don't carry their size, it's just that they can't work the miracle of making anything look decent on her.  All the clothes you are seeing in the clearance section are the ones that did not appease to any fatty's taste, most likely because its design followed a model for a human-sized individual that did not translate well to obeast-sized ones.