Sketching characters over the years has made me notice why certain proportions get dialed up to
Eleven, and Big Mom's chest is a textbook example. In 'One Piece' Oda often uses exaggeration like a visual shorthand: gigantic features = bigger personality, threat, and absurdity. Big Mom is supposed to be an overwhelming, matriarchal force whose appetite and charisma dominate every panel, so her silhouette needs to shout before she speaks.
Beyond symbolism, there are clear cartoon and caricature influences. Think of classic Western animation where body parts become exaggerated to express a trait—warmth, gluttony, menace. Oda also loves theatrical designs and costume drama; oversized shapes make her clothes, cakes, and tableaus more dramatic. Some of it is playful pandering, a wink to genre tropes, and some of it is practical storytelling: large, rounded forms let artists frame scenes, hide characters, or create comedic interactions. Personally, I find it equal parts ridiculous and brilliant—Big Mom's design tells you immediately who she is, even from the farthest panel, and that's a rare kind of visual efficiency that still makes me grin.