Nobody's body is an amorphous blob, male or female.

It's simply a matter of design and convention - clothes are designed to fit some body types, and conventional clothing styles are predicated on "degrees of freedom" of possible design that can only comfortably suit some body types without looking like a tent or a gorilla suit.

Actually "male" formal styles have more give in their degrees of freedom than informal styles for either gender, or formal styles for women, because fat men have often been suit wearers.

Still, IMO, designers ought to see "fat people of any sex" as a challenge to their ingenuity. I'd really like to see what people would come up with if effort was applied, rather than merely shifting the proportions of something designed for thin people.