...That, and Gainaxing. Some might not really mind it, but it really disrupts the elegance of a good routine. A sleek figure is preferable on these cases.
Unless its a loli game, any gymnastics game/image is going to have the girl with at least D's or larger (even some loli ones are overly well endowed). Despite the more petite figure looking more elegant the artists feel compelled to super size their busts; even some of the more infamous dfc's artists try and enlarge them (much to the malice of the characters image).