There are several factors at play here. 1- most women wear the wrong bra size. When your options are a 32band size and up and a cup size of A-D (it can go up through J in specialty stores), you take what you can get. Even women with small-looking boobs can be a DD cup, but they'll never buy it because they don't believe their breasts are that size. The cup size is a measurement of the proportion of your rib cage to your bust size, so you can have a small rib cage and small looking breasts, but still have a sizable difference in inches between the two measurements. Cup sizes are dependent on your band measurement. 2- most women are huge fucking obeasts. Who is the store going to design the bras to fit? Not the humans.