34 isn't fat. I've always been a 34. I'm also 5'10", 140 pounds. Wide ribs are a thing, you know. If you have a 26 inch band, you are very narrow in the ribs. My sister wears a a 36A. And you aren't fully correct on cup size. Cups vary based on band. Cup size is, in reality, a ration of the difference between one's rib diameter and the breasts at their fullest point. That's it (that's also why sister sizing exists. A 36B and a 34C in reality can generally fit the same woman, it will be a matter of her preference at to which she picks). A D cup just means there is about 4 inches of difference between your breast size and rib size. That's all it means. The problem is that fats have a complex about going into larger sizes - so they created things like DD, DDD and beyond. In reality, a DD is a fiction. E comes after D. But anything above D is generally regarded as a "specialty" size, so fats get a complex about them. So vanity sizing was created to make them feel better. But as fats get fatter, they still want to be able to say they're DDD, so the cups have been getting larger. Same as the bands. Fats don't want to accept the "stigma" of going into specialty sizing.