[quote=Frizan]
...why is bust size even an option?
[/quote]

If you're designing a female character's appearance, bust size is kind of a thing. 

If Chocobo were drawing this character himself, that would also be a thing; he'd have to choose what bust size to draw her with, just like he'd have to choose what height to draw her as, and how skinny/fat she is, and decide her hair style, etc. Only difference is, if he were drawing her himself, it wouldn't be an on-screen option that would draw your attention to it.

Seriously. It's just a physical trait. Whether big or small, all women come in a certain size. Whether it means anything to you or not, it is still a thing. 

I don't see why the option would strike anyone as odd.