Sorry ladies if you don't have a perfect B cup you get no representation in media.
Well, if you can find me hundreds or even dozens of very skilled actresses with an outright M or O cup being deliberatly ignored in favor of smaller-chested women, you might have a point. But thing is, B to C cups are simply far more common IRL, so of course most media representation will include them primarily.
As for animation, I don’t think you’ve ever seen any anime if you think small chested women are the rule, have you?
As for character creators in video games, you do realize that even when they allow for “boob sliders” for female bodies, there is a limit to how much most game engines can handle the sizes before the animations and textures get wonky, right?