The fanbase are the ones who gave Sanae those boobs in the first place. The fanbase can giveth and taketh what they want with their creation.
This artist also draws Sanae with huge boobs, though he also likes to draw Suwako smugly stealing parts of her appearance, including her body size, which is what she's done here.
In one instance, he's drawn Suwako reverting Sanae back to a baby, just so she can have 'uuuge boobs and a thick, curvy figure. She was most despicably pleased with herself.
