And so is a 10/12/14. However, fashion retailers overwhelmingly use size 8 models that are at least 5'8". These are not the only version of normal.
I would go further to say that some models actively look worse than curvier (but still slim) women would in the same clothes.
E.g. One top might suit a woman with big boobs, another with small boobs.
And this is before you get to tricks like pinning dresses back, changing positions etc.
Incidentally I don't actually expect them to use models like my proportions - I'm tall, with broad shoulders, hips, and massive boobs. It wouldn't help most women to see models like me.
But these days they even mostly stick a fake bump on a model for maternity wear, when it's very normal for the ribcage/chest to increase.
It's piss poor advertising, and nothing to do with entirely normal variations in size and shape.
Rihanna manages to make a range that suits lots of shapes and sizes. Shein manage to include specific garment measurements by size. No excuse for shitty advertising.